fix(backend): unread/unseen flag filter

Author: kroky

modules/imap/handler_modules.php

@@ -1270,7 +1270,7 @@ public function process() {
                 break;
             case 'flagged':
             case 'unread':
-                $filter = mb_strtoupper($this->get('list_path'));
+                $filter = $this->get('list_path') == 'unread' ? 'UNSEEN' : mb_strtoupper($this->get('list_path'));
             default:
                 if (empty($filter)) {
                     $filter = 'ALL';