Fix incorrect data retrieval is special cases

[Ozaq]

Description

Now correctly retrieves data if non-chunked extension axis is defined.

Fixes: FDB 620

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🌈🌦️📖🚧 Documentation FDB 🚧📖🌦️🌈
https://sites.ecmwf.int/docs/fdb/pull-requests/PR-270

[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.50725% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.96%. Comparing base (54f51c4) to head (fa2655b).

Files with missing lines	Patch %	Lines
src/chunked_data_view/GribExtractor.cc	0.00%	21 Missing ⚠️
tests/chunked_data_view/test_builder.cc	0.00%	5 Missing ⚠️
tests/chunked_data_view/test_view.cc	96.77%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #270      +/-   ##
===========================================
+ Coverage    70.84%   70.96%   +0.11%     
===========================================
  Files          372      372              
  Lines        23309    23465     +156     
  Branches      2454     2458       +4     
===========================================
+ Hits         16514    16652     +138     
- Misses        6795     6813      +18     

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