RespondJoinRoom in AddClient as atomic operation

to avoid missed player in rooms due to joining race condition

src/CommandHandlers/SetUserVariablesHandler.cs

@@ -47,7 +47,7 @@ class SetUserVariablesHandler : ICommandHandler {
         client.PlayerData.Fp = suvData.Get<string>("FP");
 
         Console.WriteLine($"SUV {client.Room.Name} IID: {client.ClientID}");
-        client.Room.AddClient(client);
+
         UpdatePlayersInRoom();
         SendSUVToPlayerInRoom();
     }

src/Core/Client.cs

@@ -63,7 +63,7 @@ public class Client {
         LeaveRoom();
         InvalidatePlayerData();
         Room = room;
-        Send(Room.RespondJoinRoom());
+        Room.AddClient(this);
         Send(Room.SubscribeRoom());
         UpdatePlayerUserVariables();
     }

src/Core/Room.cs

@@ -6,7 +6,7 @@ public class Room {
     static Dictionary<string, Room> rooms = new();
 
     List<Client> clients = new();
-    public object roomLock = new object();
+    protected object roomLock = new object();
 
     public int Id { get; private set; }
     public string Name { get; private set; }
@@ -38,6 +38,9 @@ public class Room {
 
     public void AddClient(Client client) {
         lock (roomLock) {
+            client.Send(RespondJoinRoom());
+            // NOTE: send RespondJoinRoom() and add client to clients as atomic operation
+            //       to make sure to client get full list of players in room
             clients.Add(client);
         }
     }