in ReactContext, de-reference the Activity in onPause() instead of onHostDestroy()

Reviewed By: andreicoman11

Differential Revision: D3004340

fb-gh-sync-id: a408cb64565e18069a291b415b1ad9d429ba8f45
shipit-source-id: a408cb64565e18069a291b415b1ad9d429ba8f45

ReactAndroid/src/main/java/com/facebook/react/bridge/ReactContext.java

@@ -156,6 +156,7 @@ public class ReactContext extends ContextWrapper {
     for (LifecycleEventListener listener : mLifecycleEventListeners) {
       listener.onHostPause();
     }
+    mCurrentActivity = null;
   }
 
   /**
@@ -166,7 +167,6 @@ public class ReactContext extends ContextWrapper {
     for (LifecycleEventListener listener : mLifecycleEventListeners) {
       listener.onHostDestroy();
     }
-    mCurrentActivity = null;
   }
 
   /**