modules/hints: NODATA answers also for non-address queries
Apparently the original implementation in 14de9110 didn't think of this. Noticed by Fantomas: https://forum.turris.cz/t/kresd-returns-nxdomain-for-local-mx-records/12991
As a part of #535 we'll most likely scrap the whole module, but that won't really happen so soon, and the fix is quite easy.