fix: error when null progress in library

[limwa]

This PR fixes an issue where library information fetching fails when there is null progress. We assume that null means 0 in the affluences API.

Review checklist

• [x] Terms and conditions reflect the current change
• [ ] Contains enough appropriate tests
• [x] If aimed at production, writes a new summary in whatsnew/whatsnew-pt-PT
• [x] Properly adds an entry in changelog.md with the change
• [x] If PR includes UI updates/additions, its description has screenshots
• [x] Behavior is as expected
• [x] Clean, well-structured code

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 11%. Comparing base (3909b97) to head (67967c5). Report is 7 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1324 +/- ## ======================================= Coverage 11% 11% ======================================= Files 268 268 Lines 7303 7303 ======================================= Hits 799 799 Misses 6504 6504 ```