added fix for frames_per_slice edge case

[pauladkisson]

Fixes #293.

[pauladkisson]

@weiglszonja, let me know is this PR fixes your issue.

[weiglszonja]

Yes, I just tested it now. Thanks!

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 79.35%. Comparing base (7aa2a63) to head (a0327b4).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #294      +/-   ##
==========================================
- Coverage   79.37%   79.35%   -0.02%     
==========================================
  Files          39       39              
  Lines        3069     3071       +2     
==========================================
+ Hits         2436     2437       +1     
- Misses        633      634       +1     

Flag	Coverage Δ
unittests	79.35% <50.00%> (-0.02%)	⬇️

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Files	Coverage Δ
...imagingextractors/scanimagetiffimagingextractor.py	98.46% <50.00%> (-0.50%)	⬇️