the presence of a DNAME record proves that the name does not exist in the zone...

the presence of a DNAME record proves that the name does not exist in the zone but as we don't want to use that for NXDMOMAIN return DNS_R_DNAME from dns_nsec_noexistnodata

(cherry picked from commit 8ef23f9f)
7 jobs for fix-synth-from-dnssec-dname-handling-v9_12 in 6 minutes and 37 seconds (queued for 3 seconds)