libdns: Fix for non-FQDN hostname.
* dirmngr/dns.c (dns_resconf_open): Clear search[0] for non-FQDN hostname.
Cherry pick from master commit:
a4a054bf14fa855715faee01a152755c4e2a74f7
- GnuPG-bug-id: T3803
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>