fix: Out-of-bounds gather in categorical->int cast

[orlp]

Fixes #18894.

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.88%. Comparing base (d3f8a5c) to head (5323061).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...-core/src/chunked_array/logical/categorical/mod.rs	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18897      +/-   ##
==========================================
- Coverage   79.89%   79.88%   -0.01%     
==========================================
  Files        1520     1520              
  Lines      206552   206552              
  Branches     2906     2906              
==========================================
- Hits       165020   165007      -13     
- Misses      40984    40997      +13     
  Partials      548      548              

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