double unlock on dns_db_newversion failure in zone.c

lib/dns/zone.c:

20483        if (zone->db != NULL) {
20484                dns_db_attach(zone->db, &db);
20485        }
     	4. unlock: isc_rwlock_unlock unlocks zone->dblock.rwlock. [show details]
     	5. Condition !!(isc_rwlock_unlock(&zone->dblock, isc_rwlocktype_read) == 0), taking true branch.
     	6. Condition !!(isc_rwlock_unlock(&zone->dblock, isc_rwlocktype_read) == 0), taking true branch.
20486        ZONEDB_UNLOCK(&zone->dblock, isc_rwlocktype_read);
     	7. Condition db == NULL, taking false branch.
20487        if (db == NULL) {
20488                goto failure;
20489        }
20490
20491        dns_db_currentversion(db, &oldver);
20492        result = dns_db_newversion(db, &newver);
     	8. Condition result != 0, taking true branch.
20493        if (result != ISC_R_SUCCESS) {
     	
CID 288540 (#1 of 1): Double unlock (LOCK)
9. double_unlock: isc_rwlock_unlock unlocks zone->dblock.rwlock while it is unlocked.
20494                ZONEDB_UNLOCK(&zone->dblock, isc_rwlocktype_read);
20495                dnssec_log(zone, ISC_LOG_ERROR,
20496                           "setnsec3param:dns_db_newversion -> %s",
20497                           dns_result_totext(result));
20498                goto failure;
20499        }