TinyMCE, wpView: bail early when the iframe node is not attached to the DOM. We can't load any HTML in it as here is no `iframe.contentWindow` in these cases.

See #36434.
Built from https://develop.svn.wordpress.org/trunk@38157


git-svn-id: http://core.svn.wordpress.org/trunk@38098 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/mce-view.js

@@ -539,6 +539,14 @@
 						dom.add( node, 'span', { 'class': 'wpview-end' } );
 					} );
 
+					// Bail if the iframe node is not attached to the DOM.
+					// Happens when the view is dragged in the editor.
+					// There is a browser restriction when iframes are moved in the DOM. They get emptied.
+					// The iframe will be rerendered after dropping the view node at the new location.
+					if ( ! iframe.contentWindow ) {
+						return;
+					}
+
 					iframeDoc = iframe.contentWindow.document;
 
 					iframeDoc.open();

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.6-beta4-38156';
+$wp_version = '4.6-beta4-38157';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.