Android: getCurrentUser shouldn't return an error - just null if no users

Author: Salakar

android/src/main/java/io/fullstack/firestack/FirestackAuth.java

@@ -72,7 +72,7 @@ private void callbackNoUser(Callback callback, Boolean isError) {
     if (isError) {
       callback.invoke(err);
     } else {
-      callback.invoke(null, err);
+      callback.invoke(null, null);
     }
   }