Core/Dungeon Finder: Add lfg state to know if a player is using lfg or lfr

- Do not allow to join battleground if using lfg/lfr

Closes issue 4189

--HG--
branch : trunk

src/server/game/Server/Protocol/Handlers/BattleGroundHandler.cpp

@@ -101,6 +101,15 @@ void WorldSession::HandleBattlemasterJoinOpcode(WorldPacket & recv_data)
 
     sLog.outDebug("WORLD: Recvd CMSG_BATTLEMASTER_JOIN Message from (GUID: %u TypeId:%u)", GUID_LOPART(guid), GuidHigh2TypeId(GUID_HIPART(guid)));
 
+    // player is using dungeon finder or raid finder
+    if (GetPlayer()->isUsingLfg())
+    {
+        WorldPacket data;
+        sBattlegroundMgr.BuildGroupJoinedBattlegroundPacket(&data, ERR_LFG_CANT_USE_BATTLEGROUND);
+        GetPlayer()->GetSession()->SendPacket(&data);
+        return;
+    }
+
     // can do this, since it's battleground, not arena
     BattlegroundQueueTypeId bgQueueTypeId = BattlegroundMgr::BGQueueTypeId(bgTypeId, 0);
     BattlegroundQueueTypeId bgQueueTypeIdRandom = BattlegroundMgr::BGQueueTypeId(BATTLEGROUND_RB, 0);