If gethostname() returned "", we used "localhost" as mock-up hostname.
However, this caused problems depending on how the local system name was
actually configured.
We have changed the mock-up hostname to "localhost-empty-hostname" now
to clearly indicate the problem. Also, we make sure that we do no
accidently try to resolve the mock-up hostname.
closes https://github.com/rsyslog/rsyslog/issues/1268