fix issue 20269

[wy65701436]

By default, use the nvd score as the primary score, and if it is unavailable, fallback to the redhat score. fix #20269

Thank you for contributing to Harbor!

Comprehensive Summary of your change

Issue being fixed

Fixes #(issue)

Please indicate you've done the following:

• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.40%. Comparing base (b7b8847) to head (a9df45b).
Report is 137 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20274      +/-   ##
==========================================
- Coverage   67.56%   66.40%   -1.17%     
==========================================
  Files         991     1039      +48     
  Lines      109181   112542    +3361     
  Branches     2719     2781      +62     
==========================================
+ Hits        73768    74730     +962     
- Misses      31449    33787    +2338     
- Partials     3964     4025      +61     

Flag	Coverage Δ
unittests	66.40% <100.00%> (-1.17%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/pkg/scan/postprocessors/report_converters.go	61.45% <100.00%> (+0.98%)	⬆️

... and 558 files with indirect coverage changes