Fix race condition when reporting mounting transactions for deallocated surfaces (#47008)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/47008

Changelog: [internal]

This code is gated anyway so there's no harm in production.

Reviewed By: javache

Differential Revision: D64322331

fbshipit-source-id: 005eb385f7e5ccd3d33e2d8c28e45b84f1537d68

packages/react-native/ReactAndroid/src/main/jni/react/fabric/FabricUIManagerBinding.cpp

@@ -121,7 +121,10 @@ void FabricUIManagerBinding::reportMount(SurfaceId surfaceId) {
         }
       }
       if (surfaceHandler != nullptr) {
-        surfaceHandler->getMountingCoordinator()->didPerformAsyncTransactions();
+        auto mountingCoordinator = surfaceHandler->getMountingCoordinator();
+        if (mountingCoordinator != nullptr) {
+          mountingCoordinator->didPerformAsyncTransactions();
+        }
       }
     } else {
       LOG(ERROR) << "FabricUIManagerBinding::reportMount: Surface with id "