[BG] Fix issues with scil_label_map

[arnaudbore]

Quick description

It should fix Aurelie issue without adding more problems.

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Type of change

Check the relevant options.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Provide data, screenshots, command line to test (if relevant)

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Checklist

• My code follows the style guidelines of this project (run autopep8)
• I added relevant citations to scripts, modules and functions docstrings and descriptions
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I moved all functions from the script file (except the argparser and main) to scilpy modules
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.58%. Comparing base (095637c) to head (0c381e9).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1275   +/-   ##
=======================================
  Coverage   72.58%   72.58%           
=======================================
  Files         294      294           
  Lines       25328    25328           
  Branches     3546     3546           
=======================================
  Hits        18385    18385           
+ Misses       5448     5447    -1     
- Partials     1495     1496    +1     

Flag	Coverage Δ
smoketests	69.77% <ø> (ø)
unittests	13.28% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
Scripts	75.43% <ø> (ø)
Library	69.19% <ø> (ø)

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[AntoineTheb]

[AntoineTheb]

Initially approved the changes and overlooked the failing tests due to previous encounters with flaky tests, but I saw that the actual cutting tests are failing. So either the tests are wrong or this PR changes the behavior of label computation.

See comment