Performance backup garbage collection potentially tries to delete same file multiple times

A cleaning task of backup.inc.php reads the file contents of a domains backup directory.
Those get compared against web_backup database table.
Backup filenames that should exist are read from web_backup table.
If there are duplicates in that table, the temp array of files to delete will have them.
The author wanted to remove those duplicates using array_unique.
It never effectively was used, as this function does not receive the value by ref but returns a new value.
This code will take the return value and use it in the comming loop which does the actual deletion.
Rare case, keeping old code does not harm.

Author: cztk

server/lib/classes/backup.inc.php

@@ -1313,8 +1313,8 @@ protected static function backups_garbage_collection($server_id, $backup_type =
                         }
                     }
                 }
-                array_unique( $untracked_backup_files );
-                foreach ($untracked_backup_files as $f) {
+                $unique_untracked_backup_files = array_unique( $untracked_backup_files );
+                foreach ($unique_untracked_backup_files as $f) {
                     $backup_file = $backup_dir . '/web' . $domain_id . '/' . $f;
                     $app->log('Backup file ' . $backup_file . ' is not contained in database, deleting this file from disk', LOGLEVEL_DEBUG);
                     @unlink($backup_file);