FIX: scorer crash if only NC and --unique

[AntoineTheb]

Quick description

The scoring script (scil_tractogram_segment_and_score.py) crashes if it only has NCs due to a restriction of np.concatenate (can't concatenate nothing).

Type of change

Check the relevant options.

• [X] 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)

To test:

Data: https://drive.google.com/file/d/1Y0faJeSrvujcwaOUUbMsKwo9-DWyWrtw/view?usp=sharing

Requires the FiberCup's scoring data to be in your working folder. Then: scil_tractogram_segment_and_score.py tractogram_Angular30FiberCup__2024-04-17-05_50_50_fibercup.trk scil_scoring_config.json crash -f -v --dilate 2 --compute_ic --unique

Checklist

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 68.15%. Comparing base (d6eddcf) to head (1996cc8).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #974 +/- ## ======================================= Coverage 68.15% 68.15% ======================================= Files 399 399 Lines 21365 21365 Branches 3229 3229 ======================================= Hits 14561 14561 Misses 5500 5500 Partials 1304 1304 ``` | [Components](https://app.codecov.io/gh/scilus/scilpy/pull/974/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | Coverage Δ | | |---|---|---| | [Scripts](https://app.codecov.io/gh/scilus/scilpy/pull/974/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | `69.19% <ø> (ø)` | | | [Library](https://app.codecov.io/gh/scilus/scilpy/pull/974/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | `66.56% <ø> (ø)` | |