Unable to save playlists with multiple paths

[Kyle Barbour]

Creating a playlist which contains tracks from more than one directory tree is possible, however, saving that playlist removes all tracks from other trees.

For example, if you have the collection "music" which contains two paths to find potential tracks:

    ~/foo
    ~/bar

and you create a playlist which has some tracks from ~/foo and some from ~/bar, that will play fine in guayadeque. However, if you attempt to save this playlist, only the tracks from ~/foo will be saved. The expected behavior is that all tracks would be saved to the playlist. There does not seem to be any way to produce the expected behavior.

System info:
- guayadeque: 0.4.5-
- kernel: 4.4.0-64-generic x86_64
- distro: Ubuntu 16.04.2 LTS xenial