[Modify] Polish it

websocket-sharp/Net/HttpListenerAsyncResult.cs

@@ -144,11 +144,13 @@ namespace WebSocketSharp.Net
         asyncResult._completed = true;
 
         var waitHandle = asyncResult._waitHandle;
+
         if (waitHandle != null)
           waitHandle.Set ();
       }
 
       var callback = asyncResult._callback;
+
       if (callback == null)
         return;