Can't resolve DNS since 2.1.17

[Gabriel Souza Franco]

Hello,

With the new backend introduced in 2.1.17 I can no longer resolve
keyserver urls, and I've traced it back to a failing SRV lookup.
For some unfathomable reason, my ISP provided router responds with
FORMERR instead of NXDOMAIN (but not for .localdomain queries,
interestingly). The failed SRV query then bubbles up, resulting in
Server indicated failure/No keyserver available errors. The old
backend seems to treat any failures as no response instead.

As a quick hack, I added FORMERR alongside every NXDOMAIN case I found,
and it seemed to work just fine. Would this be an acceptable solution?