fix possible race condition in JoinRoom

src/Core/Client.cs

@@ -9,11 +9,12 @@ public class Client {
 
     public int ClientID { get; private set; }
     public PlayerData PlayerData { get; set; } = new();
-    public Room Room { get; set; }
+    public Room Room { get; private set; }
 
     private readonly Socket socket;
     SocketBuffer socketBuffer = new();
     private volatile bool scheduledDisconnect = false;
+    private object ClientLock = new();
 
     public Client(Socket clientSocket) {
         socket = clientSocket;
@@ -60,10 +61,12 @@ public class Client {
     }
     
     public void JoinRoom(Room room) {
+        lock(ClientLock) {
             LeaveRoom();
-        InvalidatePlayerData();
-        Room = room;
+            PlayerData.IsValid = false;
             Room.AddClient(this);
+            Room = room;
+        }
         Send(Room.SubscribeRoom());
         UpdatePlayerUserVariables();
     }
@@ -79,10 +82,6 @@ public class Client {
         }
     }
 
-    public void InvalidatePlayerData() {
-        PlayerData.IsValid = false;
-    }
-
     public void Disconnect() {
         try {
             socket.Shutdown(SocketShutdown.Both);