Core/Battlegrounds: Avoid teleport players when relogin inside Strand of the Ancients

Port From (https://github.com/TrinityCore/TrinityCore/commit/a37f9b6693c74176bdbf0730e952ef7f05701cd1)

Source/Game/BattleGrounds/Zones/StrandofAncients.cs

@@ -488,7 +488,8 @@ namespace Game.BattleGrounds.Zones
 
             SendTransportInit(player);
 
-            TeleportToEntrancePosition(player);
+            if (!isInBattleground)
+                TeleportToEntrancePosition(player);
         }
 
         public override void RemovePlayer(Player player, ObjectGuid guid, Team team) { }