fix: possible null playlist in PlaylistsExporter.jsx

[morganbarrett]

playlist is sometimes null, added a check to prevent an error being thrown and the the current export being abandoned

[watsonbox]

Thanks a lot for this, do you think you could add a test? 🙏

[watsonbox]

I made the same change myself today along with a test, plus a larger scope which also fixes issues in the main listing.