Widgets: When checking for errors in Custom HTML widget, pass correct value to toggleClass() for Save button.

`toggleClass()` expects a boolean as a second argument, not an integer.

Props iCaleb.
Merges 42457 to the 4.9 branch.
Fixes #42867.
Built from https://develop.svn.wordpress.org/branches/4.9@42458


git-svn-id: http://core.svn.wordpress.org/branches/4.9@42287 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/widgets/custom-html-widgets.js

@@ -204,7 +204,7 @@ wp.customHtmlWidgets = ( function( $ ) {
 				 * @returns {void}
 				 */
 				onUpdateErrorNotice: function onUpdateErrorNotice( errorAnnotations ) {
-					control.saveButton.toggleClass( 'validation-blocked disabled', errorAnnotations.length );
+					control.saveButton.toggleClass( 'validation-blocked disabled', errorAnnotations.length > 0 );
 					control.updateErrorNotice( errorAnnotations );
 				}
 			});