Media: in wp.media.view.Toolbar.refresh(), check for a selection before iterating over models.

Props chandrapatel.
Fixes #39511.

Built from https://develop.svn.wordpress.org/trunk@40050


git-svn-id: http://core.svn.wordpress.org/trunk@39987 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/media-views.js

@@ -7724,9 +7724,11 @@ Toolbar = View.extend({
 				disabled = false;
 
 			// Prevent insertion of attachments if any of them are still uploading
-			disabled = _.some( selection.models, function( attachment ) {
-				return attachment.get('uploading') === true;
-			});
+			if ( selection && selection.models ) {
+				disabled = _.some( selection.models, function( attachment ) {
+					return attachment.get('uploading') === true;
+				});
+			}
 
 			if ( requires.selection && selection && ! selection.length ) {
 				disabled = true;