Even if hostname FQDN is configured, rsyslog internal messages generated
after rsyslog startup and before the first HUP will not necessarily have
FQDN but instead only the shortname of the local host. This commit
fixes the situation.
Special thanks to github user eciii for doing a great bug analysis
and helping us considerably to fix the issue.
closes https://github.com/rsyslog/rsyslog/issues/5218