WIP V3: don't select headers or unplayable track as next

app/classes.py

@@ -139,7 +139,7 @@ class PlaylistTrack:
         self.duration = track.duration
         self.end_time = None
         self.fade_at = track.fade_at
-        self.fade_graph = FadeCurve(track)
+        self.fade_graph = FadeCurve(track)  # TODO: speed this line up
         self.path = track.path
         self.playlist_id = plr.playlist_id
         self.plr_id = plr.id

app/playlistmodel.py

@@ -541,6 +541,12 @@ class PlaylistModel(QAbstractTableModel):
                 return
             plr = session.get(PlaylistRows, plrid)
             if plr:
+                # Check this isn't a header row
+                if plr.track is None:
+                    return
+                # Check track is readable
+                if file_is_unreadable(plr.track.path):
+                    return
                 self.next_track.set_plr(session, plr)
                 self.signals.next_track_changed_signal.emit()
                 self.invalidate_row(row_number)