Bugfix: don’t reply to bad packets with QR set
An oversight in the packet-decoding logic meant that IBDNS successfully ignores a well-formed packet with QR set, but did attempt to reply to a malformed packet with the same problem.
Also, there was an issue with the associated unit tests: they didn’t cover the case correctly, and one of the tests checking that IBDNS returns FORMERR on malformed queries actually used a response packet as test data.