Remove songs from the playlists that are not in the library before saving the library.
Remove songs from the playlists that are not in the library before saving the library.

This fixes a bug that causes the application to crash when the user adds a song from a removable device to a playlist,
then removes the device so that the song is removed from the library, but not from the playlist, and then quits the application.

punker76/Espera,flagbug/Espera