[gnome-music] playlistview: Reset song to clean on playlist change

[Marinus Schraal <mschraal src gnome org>]

commit d1404c13c8b605e9fe78f91dcc28b479d73bc682
Author: Jean Felder <jean felder gmail com>
Date:   Mon Jan 15 20:14:17 2018 +0100

    playlistview: Reset song to clean on playlist change
    
    Resets self._iter_to_clean and self._iter_to_clean_model when a new
    playlist is selected.
    Prevents an "iter_is_valid" failed error when _update_model method is
    called.
    
    Closes: #135

 gnomemusic/views/playlistview.py | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gnomemusic/views/playlistview.py b/gnomemusic/views/playlistview.py
index ef7e160..2c91d0d 100644
--- a/gnomemusic/views/playlistview.py
+++ b/gnomemusic/views/playlistview.py
@@ -476,6 +476,8 @@ class PlaylistView(BaseView):
         # use it as model, otherwise build the liststore
         self._view.set_model(None)
         self.model.clear()
+        self._iter_to_clean = None
+        self._iter_to_clean_model = None
         self._songs_count = 0
         grilo.populate_playlist_songs(playlist, self._add_song)