Restores backwards compatibility with TinyMCE plugins

ref magento/magento2#39258

Author: fballiano

lib/web/mage/adminhtml/wysiwyg/tiny_mce/plugins/magentovariable/editor_plugin.js

@@ -231,6 +231,8 @@ define([
 
                     return content;
                 });
+
+                return this.widget;
             };
 
         /**