More defensively handle initial expand

Reviewed By: jknoxville

Differential Revision: D32674423

fbshipit-source-id: 0d8216ebb9da9530c53c7209dcd18eb677c73fc3

desktop/plugins/public/layout/Inspector.tsx

@@ -281,7 +281,7 @@ export default class Inspector extends Component<Props, State> {
   // When opening the inspector for the first time, expand all elements that
   // contain only 1 child recursively.
   async performInitialExpand(element: Element | undefined): Promise<void> {
-    if (!element || !element.children.length) {
+    if (!element || !element.children || !element.children.length) {
       // element has no children so we're as deep as we can be
       return;
     }