Added handling for empty dc:subjects

[lasselehtinen]

We have some old eBooks where the dc:subject might be empty. This produces an TypeError when trying to parse getEpubVersionNumber from such ePub. I have added an array filter that removes empty values and arrays from the values and added tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.07%. Comparing base (e5d45ae) to head (197f468).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #118   +/-   ##
=========================================
  Coverage     90.07%   90.07%           
  Complexity      843      843           
=========================================
  Files            32       32           
  Lines          2589     2589           
=========================================
  Hits           2332     2332           
  Misses          257      257           

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[ewilan-riviere]

Thanks you!

[lasselehtinen]

Thanks for accepting the PR. Any estimates when you would you create a new release?

[ewilan-riviere]

Today or tomorrow, sorry for the delay!