Customize: Prevent consecutive `refresh` requests from preview from causing JS error.

Fixes "Uncaught TypeError: this.targetWindow is not a function".

See #27355.
Fixes #35866.

Built from https://develop.svn.wordpress.org/trunk@36583


git-svn-id: http://core.svn.wordpress.org/trunk@36550 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/customize-base.js

@@ -704,8 +704,9 @@ window.wp = window.wp || {};
 
 			event = event.originalEvent;
 
-			if ( ! this.targetWindow() )
+			if ( ! this.targetWindow || ! this.targetWindow() ) {
 				return;
+			}
 
 			// Check to make sure the origin is valid.
 			if ( this.origin() && event.origin !== this.origin() )

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.5-alpha-36582';
+$wp_version = '4.5-alpha-36583';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.