*Improvements in map managing.

--HG--
branch : trunk

src/game/BattleGroundMgr.cpp

@@ -1474,6 +1474,8 @@ BattleGround * BattleGroundMgr::GetBattleGroundThroughClientInstance(uint32 inst
 
 BattleGround * BattleGroundMgr::GetBattleGround(uint32 InstanceID, BattleGroundTypeId bgTypeId)
 {
+    if (!InstanceID)
+        return NULL;
     //search if needed
     BattleGroundSet::iterator itr;
     if (bgTypeId == BATTLEGROUND_TYPE_NONE)