Checking the DS at the parent only happens if dns_zone_getdnsseckeys()
returns success. However, if this function somehow fails, it can also
prevent the keymgr from running.
Before adding the check DS functionality, the keymgr should only run
if 'dns_dnssec_findmatchingkeys()' did not return an error (either
ISC_R_SUCCESS or ISC_R_NOTFOUND). After this change the correct
result code is used again.
(cherry picked from commit 07c2acf15d)
b730a65975