v1.19: Better timing for songs with long intros

If a song has a long introduction (say 10-20 seconds), it will extend the playtime to compensate. For example, if you have "maximum playtime" set to 90 seconds, but there is a 20 second introduction before any notes are placed, the song will play for 110 seconds. This is done so you can have a consistent active playtime for varying songs.