Template: Add fallback for empty containers.

Since [14031] the container can be omitted in `wp_nav_menu()`. It can not
however in `wp_page_menu()`, which creates a conflict if it is set as
the fallback, Let's make sure there is always a valid container tag.

Fixes #33974.



git-svn-id: https://develop.svn.wordpress.org/trunk@34950 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/post-template.php

@@ -1275,6 +1275,11 @@ function wp_page_menu( $args = array() ) {
 
 	$container = sanitize_text_field( $args['container'] );
 
+	// Fallback in case `wp_nav_menu()` was called without a container.
+	if ( empty( $container ) ) {
+		$container = 'div';
+	}
+
 	if ( $menu ) {
 
 		// wp_nav_menu doesn't set before and after