Missing network should error a command

[andyrooger]

If we call a command on get_iplayer and see

WARNING: no network interfaces found

appear in the output, we should take this as an error and disregard the result of the command.
For instance, the inital get versions call appears to have broken in my case with "no network interfaces found" and it was used from then on as an incomplete list of all versions, resulting in programs without a default version being unable to play or record.