[Modify] Polish it

websocket-sharp/Net/HttpListenerResponse.cs

@@ -489,8 +489,10 @@ namespace WebSocketSharp.Net
     /// </exception>
     public Stream OutputStream {
       get {
-        if (_disposed)
+        if (_disposed) {
-          throw new ObjectDisposedException (GetType ().ToString ());
+          var name = GetType ().ToString ();
+          throw new ObjectDisposedException (name);
+        }
 
         if (_outputStream == null)
           _outputStream = _context.Connection.GetResponseStream ();