Avoid a fatal error when the dir does not exist

Author: helmo

server/lib/classes/backup.inc.php

@@ -856,6 +856,10 @@ protected static function get_files($directory, $prefix_list = null, $endings_li
         if (is_null($endings_list))
             $endings_list = $default_endings_list;
 
+       if (!is_dir($directory)) {
+               return array();
+       }
+
         $dir_handle = dir($directory);
         $files = array();
         while (false !== ($entry = $dir_handle->read())) {