[Modify] Replace it

websocket-sharp/Net/HttpListener.cs

@@ -480,10 +480,8 @@ namespace WebSocketSharp.Net
         EndPointManager.RemoveListener (this);
       }
 
-      lock (_ctxRegistrySync) {
+      lock (_ctxRegistrySync)
-        if (!force)
+        cleanupContextQueue (!force);
-          sendServiceUnavailable ();
-      }
 
       cleanupContextRegistry ();
       cleanupConnections ();