Fix crash on season grouping

[ashiagr]

Description

This fixes crash on grouping by season for certain podcasts (e.g. https://pca.st/9NOf)

Fixes #961

Testing Instructions

1. Subscribe to https://pca.st/9NOf
2. Go to Pocket Casts > Profile > Settings > General > Podcast Episode Grouping, set it to None
3. View the podcast page
4. Now go back to Podcast Episode Grouping and set it to 'Season'
5. Recheck the podcast page, you should not see any crash
6. Scroll to the bottom
7. You should see a "No season" group with an episode

Screenshots or Screencast

Checklist

• If this is a user-facing change, I have added an entry in CHANGELOG.md
• I have considered whether it makes sense to add tests for my changes
• All strings that need to be localized are in modules/services/localization/src/main/res/values/strings.xml
• Any jetpack compose components I added or changed are covered by compose previews

I have tested any UI changes...

• with different themes
• with a landscape orientation
• with the device set to have a large display and font size
• for accessibility with TalkBack

[mchowning]

Looks good! Thanks for fixing this! 🙇