FIX FILTER_VALIDATE_EMAIL param is not a string

htdocs/public/ticket/ajax/ajax.php

@@ -55,7 +55,7 @@ include_once '../../../main.inc.php'; // Load $user and permissions
 
 $action = GETPOST('action', 'aZ09');
 $id = GETPOST('id', 'int');
-$email = GETPOST('email', 'custom', 0, 'FILTER_VALIDATE_EMAIL');
+$email = GETPOST('email', 'custom', 0, FILTER_VALIDATE_EMAIL);
 
 
 if (!isModEnabled('ticket')) {