validate nitpick fix: unsupported algo edge case

kr_dnskeys_trusted() semantics is changed, but I do NOT consider that
a part of public API.

Go insecure due to algorithm support even if DNSKEY is NODATA.
I can't see how that's relevant to practical usage, but I think this new
behavior makes more sense.  We still do try to fetch the DNSKEY even
though we have information about its un-usability beforehand.
I'd consider fixing that a premature optimization.
We'll still be affected if the DNSKEY query SERVFAILs or something.

Thanks to PowerDNS people for catching this!
27 jobs for <span class="ref-name">ds-algo-nodata</span> in 11 minutes and 22 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #255231
docker linux amd64
archive

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docker linux amd64
build

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docker linux amd64
build-asan

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docker
kres-gen

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  Test
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docker delayed
build:darwin

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docker linux amd64
deckard

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docker delayed
doc

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dind
docker

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docker delayed
lint:other

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docker linux amd64 delayed
lint:pedantic

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docker linux amd64
lint:scan-build

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docker linux amd64
lint:tidy

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privileged
pkg:epel-7

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privileged
pkg:fedora-29

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docker linux amd64
respdiff:basic

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docker linux amd64 delayed
test:valgrind

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  Extended
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respdiff
fwd-tls6-kresd.udp6

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fwd-udp6-kresd.udp6

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fwd-udp6-unbound.tcp6

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fwd-udp6-unbound.tls6

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fwd-udp6-unbound.udp6

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iter.tls6

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iter.udp6

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docker linux amd64
pytests

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respdiff
resperf:fwd-tls6.udp-asan

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respdiff
resperf:fwd-udp6.udp-asan

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resperf:iter.udp-asan

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