back/Application: fix fallback error template view name

src/Application.ts

@@ -200,7 +200,7 @@ export default abstract class Application implements Extendable<ApplicationCompo
                     };
                     res.render('errors/' + httpError.errorCode, locals, (err: Error | undefined, html) => {
                         if (err) {
-                            res.render('errors/Error', locals);
+                            res.render('templates/ErrorTemplate', locals);
                         } else {
                             res.send(html);
                         }