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 12353089762

Details

• 0 of 6 (0.0%) changed or added relevant lines in 1 file are covered.
• 5586 unchanged lines in 73 files lost coverage.
• Overall coverage decreased (-3.5%) to 61.253%

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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/webserver.hh	1	69.16%
pdns/recursordist/sortlist.hh	1	75.0%
pdns/iputils.hh	1	76.51%
pdns/pollmplexer.cc	1	83.66%
pdns/dnstap.cc	2	68.82%
ext/probds/murmur3.cc	2	88.24%
pdns/dnsname.hh	2	91.52%
pdns/recursordist/secpoll-recursor.cc	2	50.0%
pdns/qtype.hh	3	73.91%
pdns/recursordist/rec-tcpout.cc	3	57.14%

Totals
Change from base Build 12350291800:	-3.5%
Covered Lines:	120021
Relevant Lines:	163212

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💛 - Coveralls