luasocket bug: sending zero length udp packets has the appearance of failure

[Sam Roberts <vieuxtech@...>]

luasocket thinks it can't send zero length udp packets:

> return  socket.udp():sendto("", "127.0.0.1", 7)
nil     refused

The message doesn't mean anything, the packet is actually sent.

It doesn't have this trouble with tcp:

> return  socket.connect("127.0.0.1", 7):send("")
0       nil     nil

We work around this in our code, but it would be nice to see a fix in
the next release.

Cheers,
Sam