Backport 17797 to rec 5.2.x: Account for the existing content when parsing labels

[omoerbeek]

Short description

Backport of #17797 and #17790

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document, including the AI Policy, and added a "Signed-off-by" to my commits
• 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

[coveralls]

Coverage Report for CI Build 30798741501

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage increased (+0.005%) to 66.727%

Details

• Coverage increased (+0.005%) from the base build.
• Patch coverage: 2 uncovered changes across 1 file (13 of 15 lines covered, 86.67%).
• 26 coverage regressions across 6 files.

Uncovered Changes

File	Changed	Covered	%
pdns/dnsname.cc	7	5	71.43%
Total (2 files)	15	13	86.67%

Coverage Regressions

26 previously-covered lines in 6 files lost coverage.

File	Lines Losing Coverage	Coverage
pdns/recursordist/test-syncres_cc1.cc	13	89.28%
pdns/recursordist/syncres.cc	4	79.83%
pdns/opensslsigners.cc	3	57.47%
pdns/recursordist/pdns_recursor.cc	3	73.51%
pdns/recursordist/aggressive_nsec.cc	2	67.03%
pdns/dnssecinfra.cc	1	54.62%

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Coverage Stats

Relevant Lines:	78109
Covered Lines:	58813
Line Coverage:	75.3%
Relevant Branches:	36012
Covered Branches:	17336
Branch Coverage:	48.14%
Branches in Coverage %:	Yes
Coverage Strength:	4879949.19 hits per line

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💛 - Coveralls