Fix augmented loader with no labels

[kozlov721]

• Fixed a bug when LuxonisLoader was failing for datasets with no labels when used with augmentations
• Added tests for this use case
• Improved an error message for when user tries to load an empty dataset / view

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.53%. Comparing base (6bcbb11) to head (cb823f8).
Report is 13 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
luxonis_ml/data/loaders/luxonis_loader.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #202      +/-   ##
==========================================
+ Coverage   92.33%   92.53%   +0.19%     
==========================================
  Files          79       80       +1     
  Lines        4161     4245      +84     
==========================================
+ Hits         3842     3928      +86     
+ Misses        319      317       -2     

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