Checks whether every player expected for the current round (loaded via SlashCo.LoadCurRoundData) is connected.
Once all expected players are present it either starts a new Slasher selection or starts the round, depending on whether a Slasher still needs to be picked.
Does nothing while in the lobby, while less than 2 players are expected, or once SlashCo.CurRound.AntiLoopSpawn is set.