Add timeout

Waiting client can't hang now

DearFTP/Connection/DataConnection.cs

@@ -8,6 +8,8 @@ namespace DearFTP.Connection
 {
     class DataConnection
     {
+        public const int Timeout = 10_000;
+
         public TcpListener Listener { get; private set; }
         public TcpClient Client { get; private set; }
         public NetworkStream Stream { get; private set; }
@@ -29,16 +31,20 @@ namespace DearFTP.Connection
 
             Listener = new TcpListener(IPAddress.Any, 0);
             Listener.Start();
-
         }
 
         public void AcceptClient()
         {
-            Client = Listener.AcceptTcpClient();
+            var task = Listener.AcceptTcpClientAsync();
+
+            if (task.Wait(Timeout))
+            {
+                Client = task.Result;
                 Stream = Client.GetStream();
 
                 IsAvailable = true;
             }
+        }
         public async void AcceptClientAsync()
         {
             Client = await Listener.AcceptTcpClientAsync();