Fix for the broken Layout plugin

Summary: Fixes the broken Layout plugin in wilde. Before this fix it will just show an empty screen in the layout plugin.

Reviewed By: jknoxville

Differential Revision: D19621517

fbshipit-source-id: e10078248b95b93c6b9c87ccf4508628b6ad86bb

iOS/Plugins/FlipperKitLayoutPlugin/FlipperKitLayoutPlugin/FlipperKitLayoutPlugin.mm

@@ -72,7 +72,12 @@
 
 - (void)didConnect:(id<FlipperConnection>)connection {
   _connection = connection;
-
+  
+  if (!_rootNode) {
+    // TODO: T61384369 get rid off this if condition.
+    _rootNode = [UIApplication sharedApplication];
+  }
+  
   [SKInvalidation enableInvalidations];
 
   // Run setup logic for each descriptor