In `WP::handle_404()`, make sure `$wp_query->post` is a `WP_Post` object before cloning it.

Merges [35994] to the 4.4 branch.
Props igmoweb, swissspidy.
Fixes #35013.

Built from https://develop.svn.wordpress.org/branches/4.4@36064


git-svn-id: http://core.svn.wordpress.org/branches/4.4@36029 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp.php

@@ -609,7 +609,12 @@ class WP {
 
 			$success = true;
 			if ( is_singular() ) {
-				$p = clone $wp_query->post;
+				$p = false;
+
+				if ( $wp_query->post instanceof WP_Post ) {
+					$p = clone $wp_query->post;
+				}
+
 				// Only set X-Pingback for single posts that allow pings.
 				if ( $p && pings_open( $p ) ) {
 					@header( 'X-Pingback: ' . get_bloginfo( 'pingback_url' ) );

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4.1-alpha-36063';
+$wp_version = '4.4.1-alpha-36064';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.