Reset the song list index when a subreddit is added or removed.

[Illyism]

When I add or remove a subreddit from the selected subreddits, the song list index does not reset. In other words, I add three subreddits (A, B, C). I then listen until song 20 in the song list. I then change my selected subreddits to (X, Y, Z). The song list ignores the first 20 songs (which are now X, Y and Z) and plays song 21. I would expect the song list index to reset to the first unplayed song in the list (0 in this example).> In case of subreddit change (A,B,C) --> (B,X,Y,Z) , shuffle all unplayed B into X, Y and Z and reset index to 0.