Fixed ReactInstanceManager not getting destroyed when app moves to background

This bug caused app to start in white screen after it was relaunched since index file had already
run once.

android/app/src/main/java/com/reactnativenavigation/activities/BaseReactActivity.java

 
         // Destroy react instance manager only if there are no resumed react activities
         BaseReactActivity activity = ContextProvider.getActivityContext();
-        if (mReactInstanceManager != null && activity != null && activity.isFinishing()) {
+        if (mReactInstanceManager != null && (activity == null || activity.isFinishing())) {
             Log.i(TAG, "Destroying ReactInstanceManager");
             mReactInstanceManager.onDestroy();
         } else {