Destorying null

[bugfixerdude]

When proxying through sinopia, trying to download express. I excountered an exception in
lib/middleware.js on line 155, for some reason the res.socket was null, thus trying to destroy it resulted in a termination of sinopia.

A quick fix was:
if (res.socket != null)
return res.socket.destroy()
return ""

[rlidwka]

Thanks, I added this code to repository.

We had some issues with it as well, but I'm not sure why it happens.