[Fix] Check if can add a connection

websocket-sharp/Net/HttpConnection.cs

@@ -294,7 +294,11 @@ namespace WebSocketSharp.Net
           var lsnr = conn._context.Listener;
           if (conn._lastListener != lsnr) {
             conn.removeConnection ();
-            lsnr.AddConnection (conn);
+            if (!lsnr.AddConnection (conn)) {
+              conn.close ();
+              return;
+            }
+
             conn._lastListener = lsnr;
           }
 

websocket-sharp/Net/HttpListener.cs

@@ -503,10 +503,19 @@ namespace WebSocketSharp.Net
 
     #region Internal Methods
 
-    internal void AddConnection (HttpConnection connection)
+    internal bool AddConnection (HttpConnection connection)
     {
-      lock (_connectionsSync)
+      if (!_listening)
+        return false;
+
+      lock (_connectionsSync) {
+        if (!_listening)
+          return false;
+
         _connections[connection] = connection;
+      }
+
+      return true;
     }
 
     internal bool Authenticate (HttpListenerContext context)