Fix for Bug#28963 "Missing DBUG_RETURN message when stopping event

scheduler".
Add missing DBUG_VOID_RETURN


sql/event_scheduler.cc:
  Fix for Bug#28963 "Missing DBUG_RETURN message when stopping event scheduler"

sql/event_scheduler.cc

@@ -326,6 +326,8 @@ end:
 
   delete event;
   deinit_event_thread(thd);
+
+  DBUG_VOID_RETURN;
 }