Game/GameObject: Fix Spellcast for 'Silithyst'

by @Whoami
updates #14637

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

@@ -1757,6 +1757,9 @@ void GameObject::Use(Unit* user)
         return;
     }
 
+    if (Player* player = user->ToPlayer())
+        sOutdoorPvPMgr->HandleCustomSpell(player, spellId, this);
+
     if (spellCaster)
         spellCaster->CastSpell(user, spellInfo, triggered);
     else