[Modify] Polish it

Author: sta

websocket-sharp/Net/HttpListenerContext.cs

@@ -236,7 +236,7 @@ internal void SendError ()
                       );
 
         var enc = Encoding.UTF8;
-        var entity = enc.GetBytes (content.ToString ());
+        var entity = enc.GetBytes (content);
         _response.ContentEncoding = enc;
         _response.ContentLength64 = entity.LongLength;