Handle case where IOS can send active child -1

Summary:
Sometimes iOS can return active child -1,  which is causing some crashes on desktop, (see the tasks) this is a client bug but the desktop shouldnt crash none the less

seems to occur only sometimes only on fboios

Reviewed By: lblasa

Differential Revision: D46894387

fbshipit-source-id: f9c34fe8fb32691486455224f82bed9c3dce6cef

desktop/plugins/public/ui-debugger/components/Visualization2D.tsx

@@ -194,7 +194,11 @@ function Visualization2DNode({
 
   //if there is an active child don't draw the other children
   //this means we don't draw overlapping activities / tabs etc
-  if (node.activeChildIdx && node.activeChildIdx < node.children.length) {
+  if (
+    node.activeChildIdx != null &&
+    node.activeChildIdx >= 0 &&
+    node.activeChildIdx < node.children.length
+  ) {
     nestedChildren = [node.children[node.activeChildIdx]];
   } else {
     nestedChildren = node.children;