hopefully Out of scope observable fix

from https://github.com/jonataslaw/getx/pull/2522/commits/8002d5fa242472bbcb74d5ea025d2f17468530d3

@@ -178,7 +178,7 @@ class Notifier {
     if (data.disposers.isEmpty && data.throwException) {
       throw ObxError();
     }
-    _notifyData = data;
+    _notifyData = null;
     return result;
   }
 }