Nights don't get skipped when the last player is set to specator mode

When almost all players on a server/OpenToLan-world are asleep and the last player is set to spectator mode the all-players-sleeping flag is not updated, causing it to stay night.

What I expected to happen was...:
When all players that are not spectators are asleep, the night should get skipped.

What actually happened was...:
It stayed night after the last player was set to spectator mode.

Steps to Reproduce:
1. Get on a server with one other player.
2. /gamemode 1 @a
3. /time set night
4. Player 1 lies down in a bed.
5. Player 2 sets his gamemode to spectator mode. (/gamemode 3)
6. The night won't get skipped.

Video: https://youtu.be/ZkI3uU7hoBA?t=39s