Fix nav walker infinite loop

inc/nav-walker.php

@@ -323,7 +323,7 @@ function my_wp_nav_menu_objects_sub_menu( $sorted_menu_items, $args ) {
 		$level = 0;
 		$stack = array('0');
 		foreach($sorted_menu_items as $key => $menu_item) {
-			while($menu_item->menu_item_parent != array_pop($stack)) {
+			while(in_array($menu_item->menu_item_parent, $stack) && $menu_item->menu_item_parent != array_pop($stack)) {
 				$level--;
 			}   
 			$level++;