Web player crashes when attempting to play album on repeat with no available songs

[spamcannon]

To reproduce:

1. Have a saved album.

2. Remove the album from the spotify service.

3. Go to your list of saved albums.

4. Set the "repeat" settings to "loop enabled".

5. Attempt to play the album.

6. Watch the web player become unresponsive and then show an error page.

What's probably going on is that the web player attempts to play the next song when the current one in the playlist is unavailable. If you wind up with a playlist that only contains unavailable songs, this doesn't ever result in playing a song.