#181564 follow up patch by webernet: fix a notice introduced by the earlier patch committed

includes/menu.inc

@@ -584,6 +584,7 @@ function menu_tree($menu_name = 'navigation') {
  */
 function menu_tree_output($tree) {
   $output = '';
+  $items = array();
 
   // Pull out just the menu items we are going to render so that we 
   // get an accurate count for the first/last classes.