Core/Entities: fix a crash that would happen whenever a player logged back in to an ended arena battle. Thanks Nawuko for the input

Closes #17825

src/server/game/Entities/Player/Player.cpp

@@ -17113,7 +17113,10 @@ bool Player::LoadFromDB(ObjectGuid guid, SQLQueryHolder *holder)
         {
             // leave bg
             if (player_at_bg)
+            {
+                player_at_bg = false;
                 currentBg->RemovePlayerAtLeave(GetGUID(), false, true);
+            }
 
             // Do not look for instance if bg not found
             WorldLocation const& _loc = GetBattlegroundEntryPoint();