Duet in songlist is wrong after switching singers + changing number of players

[barbeque-squared]

How to reproduce:

• Go to the songlist with 4 players
• Select any duet
• Space to switch singers
• M -> Song -> Change players -> Set it to 3 and Enter
• At this point you can just Escape until you're on the songlist again

Other player numbers will probably also work, this just makes it extremely obvious (assuming you're using a single screen):

I don't know if the swapped players are supposed to stick around after a song ends, but either way this looks very nice! Almost certainly related to #963

It's likely this also happens when only changing the number of players, but this just makes it more obvious.