socket_can_read doesn't work when the socket's fd is 0

[nramon]

First of all, thanks for fping. It's a great piece of software!

Yesterday I saw it fail when called from a script. The problem was that socket_can_read doesn't work when the socket's file descriptor is 0, because it uses this value to signal a timeout.

This behaviour can be reproduced fairly easily:

# bash -c 'exec 0<&-; src/fping 127.0.0.1'
127.0.0.1 is unreachable

I've submitted a pull request (#124) that fixes the problem:

# bash -c 'exec 0<&-; src/fping 127.0.0.1'
127.0.0.1 is alive

Best regards.