Fix NPE in LayoutInspector

Summary: Fixed a potential NPE that could happen in layout editor.

Reviewed By: passy

Differential Revision: D30870185

fbshipit-source-id: 3ae5860ce63761336d8bc508dd8eff761a5ab1f8

desktop/plugins/public/layout/Inspector.tsx

@@ -318,6 +318,9 @@ export default class Inspector extends Component<Props, State> {
           forAccessibilityEvent,
           selected: false,
         });
+      if (!elements) {
+        return [];
+      }
       elements.forEach((e) => this.updateElement(e.id, e));
       return elements;
     } else {