Bail when there is neither a menu, or a fallback. props ptahdunbar, fixes #13006.

git-svn-id: https://develop.svn.wordpress.org/trunk@14415 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/nav-menu-template.php

@@ -220,6 +220,10 @@ function wp_nav_menu( $args = array() ) {
 		}
 	}
 
+	// If no fallback function was specified and the menu doesn't exists, bail.
+	if ( !$menu || is_wp_error($menu) )
+		return false;
+
 	$nav_menu = '';
 	$items = '';
 	$container_allowedtags = apply_filters( 'wp_nav_menu_container_allowedtags', array( 'div', 'p', 'nav' ) );