Fix edge case when we enqueue a pending event to views on stopped surface

Summary:
This diff address an edge case when the pending events are enqueued when the surface is stopped. In this case we will reset map that holds view state to null, which will cause NPE.

Changelog:
[Android][Fixed] - Fix edge case when we enqueue a pending event to views on stopped surface

Reviewed By: javache, gorodscy

Differential Revision: D36912786

fbshipit-source-id: 3ae5a4b08a0a6bf55538d69ac80a101c2c3d899a

ReactAndroid/src/main/java/com/facebook/react/fabric/mounting/SurfaceMountingManager.java

@@ -1092,6 +1092,12 @@ public class SurfaceMountingManager {
   public void enqueuePendingEvent(int reactTag, ViewEvent viewEvent) {
     UiThreadUtil.assertOnUiThread();
 
+    // When the surface stopped we will reset the view state map. We are not going to enqueue
+    // pending events as they are not expected to be dispatched anyways.
+    if (mTagToViewState == null) {
+      return;
+    }
+
     ViewState viewState = mTagToViewState.get(reactTag);
     if (viewState == null) {
       // Cannot queue event without view state. Do nothing here.