Fix for update 20230613.php

Had an issue that was affecting the database update for mysql, current code is specific to mariadb. Updated code should work for both mysql and mariadb.

updates/20230613.php

@@ -16,9 +16,12 @@ public function items()
     public function run()
     {
         // Add a file location column to playlists to use when storing thumbnails.
-        $this->db->query('ALTER TABLE `playlists` ADD COLUMN IF NOT EXISTS `file_location` VARCHAR(2) NOT NULL AFTER `name`;');
-        if ($this->db->error()) {
-            return false;
+        if (! $this->db->column_exists('playlists', 'file_location')) {
+            $this->db->query('ALTER TABLE `playlists` ADD COLUMN `file_location` VARCHAR(2) NOT NULL AFTER `name`;');
+            if ($this->db->error()) {
+                echo $this->db->error(); //Debug output
+                return false;
+            }
         }
 
         // Add a random location to all previously existing playlists and create their directories.