rec: fix a difference between record-cache hit and miss in some ServFail results

[omoerbeek]

Short description

Specifically when the max CNAME chain length is exceeded (with QName Minimization enabled), but there are likely other cases.

Fixes #14310

Checklist

I have:

• [X] read the CONTRIBUTING.md document
• [X] compiled this code
• [X] tested this code
• [ ] included documentation (including possible behaviour changes)
• [X] documented the code
• [ ] added or modified regression test(s)
• [X] added or modified unit test(s)

[coveralls]

Pull Request Test Coverage Report for Build 11686424851

Details

• 13 of 13 (100.0%) changed or added relevant lines in 2 files are covered.
• 5225 unchanged lines in 76 files lost coverage.
• Overall coverage decreased (-0.06%) to 64.634%

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Files with Coverage Reduction	New Missed Lines	%
pdns/webserver.hh	1	69.16%
pdns/recursordist/sortlist.hh	1	75.0%
pdns/iputils.hh	1	78.25%
pdns/dnstap.cc	2	70.97%
ext/probds/murmur3.cc	2	94.12%
pdns/sstuff.hh	2	56.83%
pdns/dnsname.hh	2	91.68%
pdns/opensslsigners.cc	2	61.07%
pdns/recursordist/secpoll-recursor.cc	2	51.02%
pdns/rcpgenerator.cc	2	89.77%
<!--	Total:	5225		-->

Totals
Change from base Build 11681769272:	-0.06%
Covered Lines:	125342
Relevant Lines:	163095

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💛 - Coveralls