Don't copy header rows when moving unplayed tracks

Fixes #222

app/playlistmodel.py

@@ -570,7 +570,11 @@ class PlaylistModel(QAbstractTableModel):
         Return a list of unplayed row numbers
         """
 
-        result = [a.plr_rownum for a in self.playlist_rows.values() if not a.played]
+        result = [
+            a.plr_rownum
+            for a in self.playlist_rows.values()
+            if not a.played and a.track_id is not None
+        ]
         log.info(f"get_unplayed_rows() returned: {result=}")
         return result