Before, next_song returns no song when the following songs are bad. For example, the playlist has [valid_song1, valid_song2, bad_song1, bad_song2] and the current song is valid_song2. At the this time, next_song return None before. After this PR, next_song returns valid_song1.
Before, next_song returns no song when the following songs are bad. For example, the playlist has [valid_song1, valid_song2, bad_song1, bad_song2] and the current song is valid_song2. At the this time, next_song return None before. After this PR, next_song returns valid_song1.