Ensure pixel data is valid when validation is skipped

[rkm]

This is a follow-up to #429.

While we now skip validation of pixel data for selected image types, we still want to ensure that the pixel data elements are valid when opened via DicomImage. This change first checks the SOPClassUID.IsImageStorage value to ensure we only look for pixel data in files which should contain images, and not e.g., SRs.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9ce9bd2) 39.31% compared to head (f1509ae) 39.57%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #430      +/-   ##
==========================================
+ Coverage   39.31%   39.57%   +0.25%     
==========================================
  Files          67       67              
  Lines        3828     3841      +13     
  Branches      514      515       +1     
==========================================
+ Hits         1505     1520      +15     
  Misses       2227     2227              
+ Partials       96       94       -2     

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