[IMP] web_editor: remove message before leaving page if editor is destro

closes odoo/odoo#62630

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/web_editor/static/src/js/wysiwyg/wysiwyg.js

@@ -450,6 +450,9 @@ var Wysiwyg = Widget.extend({
      * @override
      */
     destroy: function () {
+        // Saving the content of the editor is not possible after destroy,
+        // so there's no need to keep the pop-up warning in this case.
+        window.onbeforeunload = null;
         this.editor.stop();
         this._super();
     },