Fix nodeHandle crash

Summary:
It's supposed to take a component or a handle, per the arg name, so switch on the type (and handle `null`).

`FlatListExample` no longer crashes.

Reviewed By: bvaughn, sebmarkbage

Differential Revision: D4752619

fbshipit-source-id: 720421f648f7c2049b5cc44f006484eb47d22d86

Libraries/Renderer/src/renderers/native/ReactNativeStack.js

@@ -37,7 +37,11 @@ var ReactNative = {
   // The injected findNodeHandle() strategy returns the instance wrapper though.
   // See NativeMethodsMixin#setNativeProps for more info on why this is done.
   findNodeHandle(componentOrHandle : any) : ?number {
-    return findNodeHandle(componentOrHandle).getHostNode();
+    const nodeHandle = findNodeHandle(componentOrHandle);
+    if (nodeHandle == null || typeof nodeHandle === 'number') {
+      return nodeHandle;
+    }
+    return nodeHandle.getHostNode();
   },
 
   render: render,