Posts, Post Types: Correctly show hierarchical post type hierarchy in admin.

In [44185], a bug was introduced where hierarchical post types would not display in the correct default order (hierarchically).

This was caused by a `! isset()` check, which returned `false` after [44185], causing the correct default value to not be applied. This switches that conditional to use an `empty()` check, ignoring the new empty string assignment that was added to prevent a PHP notice when `compact()` is called.

Props davidbinda.
Fixes #45711.
Built from https://develop.svn.wordpress.org/trunk@44338


git-svn-id: http://core.svn.wordpress.org/trunk@44168 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/post.php

@@ -1157,7 +1157,7 @@ function wp_edit_posts_query( $q = false ) {
 	$query = compact( 'post_type', 'post_status', 'perm', 'order', 'orderby', 'posts_per_page' );
 
 	// Hierarchical types require special args.
-	if ( is_post_type_hierarchical( $post_type ) && ! isset( $orderby ) ) {
+	if ( is_post_type_hierarchical( $post_type ) && empty( $orderby ) ) {
 		$query['orderby']                = 'menu_order title';
 		$query['order']                  = 'asc';
 		$query['posts_per_page']         = -1;

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44336';
+$wp_version = '5.1-alpha-44338';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.