auth: prevent createReverse6 from generating illegal IDN record

[BozhanL]

Short description

createReverse6 will insert or push '0' to the converted address, so that dig will not treated it as an illegal IDN.
Closes #7524

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master

[Habbie]

awesome! thank you. One very small nit.

[coveralls]

Pull Request Test Coverage Report for Build 12840316338

Details

• 0 of 6 (0.0%) changed or added relevant lines in 1 file are covered.
• 28 unchanged lines in 10 files lost coverage.
• Overall coverage increased (+0.01%) to 64.707%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pdns/lua-record.cc	0	6	0.0%

Files with Coverage Reduction	New Missed Lines	%
pdns/misc.cc	2	63.15%
pdns/distributor.hh	2	51.86%
pdns/backends/gsql/gsqlbackend.hh	2	97.71%
modules/lmdbbackend/lmdbbackend.cc	2	73.66%
pdns/misc.hh	3	87.62%
pdns/packethandler.cc	3	72.79%
pdns/iputils.cc	3	56.84%
pdns/opensslsigners.cc	3	61.41%
pdns/rcpgenerator.cc	3	90.37%
pdns/signingpipe.cc	5	86.06%

Totals
Change from base Build 12832418127:	0.01%
Covered Lines:	127810
Relevant Lines:	166441

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💛 - Coveralls