core: fix a possible crash if given an empty IP4 config
update_system_hostname() was bailing out if (there is no IP4 config or the IP4 config has no addresses) AND (there is no IP6 config or the IP6 config has no addresses), but it would then hit an assertion and crash if there was a valid IP6 config along with an IP4 config with no addresses. Fix that and get rid of some redundancy. Sort of pointed out by Coverity.
Showing with 5 additions and 17 deletions