Switch to using safer UpdateState mechanism

Summary:
Update FabricViewStateManager so that the caller can bail out of updates by returning null.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D22966024

fbshipit-source-id: 31cd9ec8a9a9918fbb94844e30ed1a2fcc61997d

ReactAndroid/src/main/java/com/facebook/react/uimanager/FabricViewStateManager.java

@@ -78,8 +78,12 @@ public class FabricViewStateManager {
             }
           };
     }
+    @Nullable WritableMap stateUpdate = stateUpdateCallback.getStateUpdate();
+    if (stateUpdate == null) {
+      return;
+    }
     stateWrapper.updateState(
-        stateUpdateCallback.getStateUpdate(),
+        stateUpdate,
         // Failure callback - this is run if the updateState call fails
         failureRunnable);
   }