Core/GameObject: implement gaining experience from unlocking chests

* this handles gathering experience as well as getting some extra xp from opening hidden treasure chests

src/server/game/Entities/GameObject/GameObject.cpp

@@ -895,7 +895,7 @@ void GameObject::Update(uint32 diff)
                         }
 
                         m_respawnTime = 0;
-                        m_SkillupList.clear();
+                        _tappingPlayers.clear();
                         m_usetimes = 0;
 
                         switch (GetGoType())