getRecords should not raise an error when there are no records (e.g. no AAAA)

Hello,

If the lookup is successful but does not contain data, getRecords raises an error which in turn prevents the code from doing anything (print error and sys.exit).

$ ./swede verify stalkr.net
Received the following record for name _443._tcp.stalkr.net.:
        Usage:                          1 (End-Entity Constraint + chain to CA)
        Selector:                       1 (SubjectPublicKeyInfo)
        Matching Type:                  1 (SHA-256)
        Certificate for Association:    a0e5e59adc9932a4d9977fe37c50da32d12119fe1478ffca89620bfa3206b750
This record is valid (well-formed).
Attempting to verify the record with the TLS service...
Unable to resolve stalkr.net.: Unsuccesful lookup or no data returned for rrtype 28.

rrtype 28 is AAAA and indeed there is no AAAA for stalkr.net:
$ host -t AAAA stalkr.net
stalkr.net has no AAAA record

The proposed change returns an empty list when the lookup is successful but there is no record:
$ ./swede verify stalkr.net
Received the following record for name _443._tcp.stalkr.net.:
        Usage:                          1 (End-Entity Constraint + chain to CA)
        Selector:                       1 (SubjectPublicKeyInfo)
        Matching Type:                  1 (SHA-256)
        Certificate for Association:    a0e5e59adc9932a4d9977fe37c50da32d12119fe1478ffca89620bfa3206b750
This record is valid (well-formed).
Attempting to verify the record with the TLS service...
Got the following IP: 91.121.51.205
[...]

Cheers,
StalkR