non-library store tracks in linked static playlists do not get synced

[simon-weber]

https://github.com/simon-weber/Autoplaylists-for-Google-Music/issues/117#issuecomment-269149723 describes an unexpected situation:

• create a static playlist by adding a store track that's not in your library
• link it to an autoplaylist
• -> the autoplaylist does not contain that track

This is because non-library tracks are never put into the track cache, so they don't show up when querying for them. Fixing this is troublesome because of https://github.com/simon-weber/gmusicapi/issues/182 and https://github.com/simon-weber/Autoplaylists-for-Google-Music/issues/97#issuecomment-261733918: this may end up getting blocked on Google.

If that ends up being the case, we could at least detect these tracks. It'd probably be relatively straightforward to even support a prompt to add them all to the user's library.

[simon-weber]

Someone recently ran into this on the mailing list.

[simon-weber]

It looks like this is affected more people now (maybe playlist linking is becoming more popular?). I'll take another look to see if Google returns full metadata for get_track_info. If not, I'll add a warning when querying a playlist affected by this.

[simon-weber]

https://github.com/simon-weber/Autoplaylists-for-Google-Music/issues/181#issuecomment-354689197 notes how to batch-add tracks to the library.