Fix CID 332468: Memory - illegal accesses (UNINIT)

Fix CID 332468: Memory - illegal accesses (UNINIT)

*** CID 332468:  Memory - illegal accesses  (UNINIT)
/lib/dns/zone.c: 6613 in dns_zone_getdnsseckeys()
6607                 ISC_LIST_UNLINK(dnskeys, k1, link);
6608                 ISC_LIST_APPEND(*keys, k1, link);
6609             }
6610         }
6611     6612     failure:
>>>     CID 332468:  Memory - illegal accesses  (UNINIT)
>>>     Using uninitialized value "keyset.methods" when calling
>>>     "dns_rdataset_isassociated".
6613         if (dns_rdataset_isassociated(&keyset)) {
6614             dns_rdataset_disassociate(&keyset);
6615         }
6616         if (node != NULL) {
6617             dns_db_detachnode(db, &node);
6618         }

Fix by initializing the 'keyset' with 'dns_rdataset_init'.