Upload form php che restituisce un errore dentro ad un ciclo che è false

Ragazi, come da titolo, ho un problema in un form PHP.

In poche parole, ho inserito un messaggio di errore dentro ad una condizione e ogni volta che lascio vuoto mi mostra sempre l'errore. Ecco il codice:

    if(isset($_POST['send_mod']))
    {
        $band_id = isset($bands_edit);
        $band_name =  htmlspecialchars(trim($_POST['name']));
        $band_letter = ((strpos(strtolower($band_name), 'the ') === 0) ? substr((substr($band_name, 4, -1) . ', ' . substr($band_name, 0, 4)),0,1) : substr($band_name, 0, 1));
        $band_genre = '';
        for ($i=0; $i < sizeof($HTTP_POST_VARS['genre']); $i++)
        {
            $band_genre .= $HTTP_POST_VARS['genre'][$i]." ";
        };
        $band_label = $_POST['label'];
        $band_city_formed = htmlspecialchars(trim($_POST['city']));
        $band_date_formed = htmlspecialchars(trim($_POST['date']));
        $band_name_album = htmlspecialchars(trim($_POST['name_album']));
        $band_date_album = htmlspecialchars(trim($_POST['date_album']));
        
        $band_website = str_replace('http://', '', htmlspecialchars(trim($_POST['website'])));
        $band_myspace = str_replace('http://', '', htmlspecialchars(trim($_POST['myspace'])));

        for($i = 1; $i <= 10; $i++)
        {
            $band_member_name = $band_names['name'][$i] = $_POST['name_' . $i];
            $band_member_part = $band_parts['part'][$i] = $_POST['part_' . $i];
            $band_delete_member[$i] = (isset($_POST['delete_member_' . $i])) ? true : false;
        }

        $band_bio = htmlspecialchars(trim($_POST['bio']));

        if(isset($_FILES['band_logo']))
        {
            $upload_dir = IP_ROOT_PATH . 'images/bands/' . strtolower($band_letter) . '/';
            $filetypes = 'jpg,gif,png';
            $maxsize = (1600 * 1200);
            $filename = strtolower($_FILES['band_logo']['name']);
            $types = explode(',', $filetypes);
            $file = explode('.', $filename);
            $extension = $file[count($file) - 1];
            $filename = substr($filename, 0, strlen($filename) - strlen($extension) - 1);
    
            if(!in_array($extension, $types))
            {
                message_die(GENERAL_MESSAGE, $lang['Upload_File_Type_Allowed'] . ': ' . str_replace(',', ', ', $filetypes) . '.');
            }
    
            if (is_dir($upload_dir))
            {
                $filename = make_url_friendly($band_name);
            }
            else
            {
                $dir_creation = mkdir($upload_dir, 0777);
                if ($dir_creation)
                {
                    $filename = make_url_friendly($band_name);
                }
                else
                {
                    $filename = make_url_friendly($band_name);
                }
            }

            $filename_tmp = $_FILES['band_logo']['tmp_name'];
            $file_size = $_FILES['band_logo']['size'];

            if($file_size > $maxsize)
            {
                message_die(GENERAL_MESSAGE, $lang['Upload_File_Too_Big'] . ' ' . ($maxsize / 1000) . 'KB');
            }

            if(is_uploaded_file($filename_tmp))
            {
                move_uploaded_file($filename_tmp, $upload_dir . $filename . '.' . $extension);
            }
            else
            {
                message_die(GENERAL_MESSAGE, 'Impossibile caricare immagine in ' . $upload_dir);
            }

            $pic_size = @getimagesize($upload_dir . $filename . '.' . $extension);
            $logo_width = $pic_size[0];
            $logo_height = $pic_size[1];

            if($pic_size == false)
            {
                @unlink($upload_dir . $filename . '.' . $extension);
                message_die(GENERAL_MESSAGE, $lang['Upload_File_Type_Allowed'] . ': ' . str_replace(',', ', ', $filetypes) . '.');
            }
        }
    } 

La riga "incriminata" è questa:

            if(!in_array($extension, $types))
            {
                message_die(GENERAL_MESSAGE, $lang['Upload_File_Type_Allowed'] . ': ' . str_replace(',', ', ', $filetypes) . '.');
            } 

Questo messaggio viene mostrato se non inserisco un file nell'input, anche se la condizione if(isset($_FILES['band_logo'])) è false.

Dato che si trova in questa condizione, come è possibile che venga elaborata?

Grazie in anticipo ad eventuali risposte

Sostituisci

 if(isset($_POST['send_mod'])) 

con

 if(!empty($_POST['send_mod'])) 

Quella variabile è settata, solo che è vuota. Una variabile può essere 'settata' ma vuota. Ed è proprio quello il motivo per cui ti si vede l'errore lo stesso.

Grazie stoner, ho modificato così:

    if(!empty($_POST['send_mod']))
    {
        $upload_dir = IP_ROOT_PATH . 'images/bands/' . strtolower($band_letter) . '/';
        $filetypes = 'jpg,gif,png';
        $maxsize = (1600 * 1200);

        $band_id = isset($bands_edit);
        $band_name =  htmlspecialchars(trim($_POST['name']));
        $band_letter = ((strpos(strtolower($band_name), 'the ') === 0) ? substr((substr($band_name, 4, -1) . ', ' . substr($band_name, 0, 4)),0,1) : substr($band_name, 0, 1));
        $band_genre = '';
        for ($i=0; $i < sizeof($HTTP_POST_VARS['genre']); $i++)
        {
            $band_genre .= $HTTP_POST_VARS['genre'][$i]." ";
        };
        $band_label = $_POST['label'];
        $band_city_formed = htmlspecialchars(trim($_POST['city']));
        $band_date_formed = htmlspecialchars(trim($_POST['date']));
        $band_name_album = htmlspecialchars(trim($_POST['name_album']));
        $band_date_album = htmlspecialchars(trim($_POST['date_album']));
        
        $band_website = str_replace('http://', '', htmlspecialchars(trim($_POST['website'])));
        $band_myspace = str_replace('http://', '', htmlspecialchars(trim($_POST['myspace'])));

        for($i = 1; $i <= 10; $i++)
        {
            $band_member_name = $band_names['name'][$i] = $_POST['name_' . $i];
            $band_member_part = $band_parts['part'][$i] = $_POST['part_' . $i];
            $band_delete_member[$i] = (isset($_POST['delete_member_' . $i])) ? true : false;
        }

        $band_bio = htmlspecialchars(trim($_POST['bio']));

        if(!(empty($_FILES['band_logo'])))
        {
            $filename = strtolower($_FILES['band_logo']['name']);
            $types = explode(',', $filetypes);
            $file = explode('.', $filename);
            $extension = $file[count($file) - 1];
            $filename = substr($filename, 0, strlen($filename) - strlen($extension) - 1);
    
            if(!in_array($extension, $types))
            {
                message_die(GENERAL_MESSAGE, $lang['Upload_File_Type_Allowed'] . ': ' . str_replace(',', ', ', $filetypes) . '.');
            }
    
            if (is_dir($upload_dir))
            {
                $filename = make_url_friendly($band_name);
            }
            else
            {
                $dir_creation = mkdir($upload_dir, 0777);
                $filename = make_url_friendly($band_name);
            }

            $filename_tmp = $_FILES['band_logo']['tmp_name'];
            $file_size = $_FILES['band_logo']['size'];

            if($file_size > $maxsize)
            {
                message_die(GENERAL_MESSAGE, $lang['Upload_File_Too_Big'] . ' ' . ($maxsize / 1000) . 'KB');
            }

            if(is_uploaded_file($filename_tmp))
            {
                move_uploaded_file($filename_tmp, $upload_dir . $filename . '.' . $extension);
                $old_logo_ext = $row['logo_ext'];
                $old_band_name = make_url_friendly($row['name']);
                if($old_logo_ext != $extension)
                {
                    unlink($upload_dir . $old_band_name . '.' . $old_logo_ext);
                }
            }
            else
            {
                message_die(GENERAL_MESSAGE, 'Impossibile caricare immagine in ' . $upload_dir);
            }

            $pic_size = @getimagesize($upload_dir . $filename . '.' . $extension);
            $logo_width = $pic_size[0];
            $logo_height = $pic_size[1];

            if($pic_size == false)
            {
                @unlink($upload_dir . $filename . '.' . $extension);
                message_die(GENERAL_MESSAGE, $lang['Upload_File_Type_Allowed'] . ': ' . str_replace(',', ', ', $filetypes) . '.');
            }
        }
        elseif($band_name != $row['name'])
        {
            rename($upload_dir . make_url_friendly($row['name']) . '.' . $row['logo_ext'], $upload_dir . make_url_friendly($band_name) . '.' . $row['logo_ext']);
        }
    } 

Ma mi viene mostrato sempre quell'errore

Non può entrare in quel ramo se la condizione è falsa. Metti una stampa subito dopo l'if e vedi se effettivamente entra.