Don't throw when accessing view config

Summary:
It turns out that it's expected in certain cases for `UIManager.getViewManagerConfig` to return null: https://fburl.com/4h4pqtd7

Instead of throwing when you try to call that function, let's log something and return null.

Reviewed By: fkgozali

Differential Revision: D15791367

fbshipit-source-id: 71cf14071d877070b4f8b2d72eaa2f10beac38db

Libraries/ReactNative/DummyUIManager.js

@@ -11,9 +11,10 @@
 
 module.exports = {
   getViewManagerConfig: (viewManagerName: string) => {
-    throw new Error(
-      'Attempting to get config for view manager ' + viewManagerName,
+    console.warn(
+      'Attempting to get config for view manager: ' + viewManagerName,
     );
+    return null;
   },
   getConstants: () => ({}),
   getConstantsForViewManager: (viewManagerName: string) => {},