Menus: Fix the Custom Links text fallback.

When adding a Custom Link and leaving the "Link Text" field empty, WordPress used to set a default fallback text: "Menu Item".

The changes in [36379] broke this behavior making the fallback text: `(Pending)`, with a leading space.

Pending major refactoring of the Menus page (which is going to use a block-based user interface) this change just restores the original behavior by adding the fallback text to the related AJAX response.

Props christophherr, Fencer04, thakkarhardik, backermann1978, audrasjb.
Merges [45727] to the 5.2 branch.
Fixes #38415.
Built from https://develop.svn.wordpress.org/branches/5.2@45828


git-svn-id: http://core.svn.wordpress.org/branches/5.2@45639 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/ajax-actions.php

@@ -1423,6 +1423,7 @@ function wp_ajax_add_menu_item() {
 		$menu_obj = get_post( $menu_item_id );
 		if ( ! empty( $menu_obj->ID ) ) {
 			$menu_obj        = wp_setup_nav_menu_item( $menu_obj );
+			$menu_obj->title = empty( $menu_obj->title ) ? __( 'Menu Item' ) : $menu_obj->title;
 			$menu_obj->label = $menu_obj->title; // don't show "(pending)" in ajax-added items
 			$menu_items[]    = $menu_obj;
 		}

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.2.3-alpha-45666';
+$wp_version = '5.2.3-alpha-45828';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.