When modifying a rewindable action from outside of its parent, it may set a tick in one loop, but not in the next one. For example, the player hits a spike, and the spike sets the RewindableAction for tick 15. On the next loop, the player doesn't hit the spike on tick 15, but is also not simulated for tick 15 since it doesn't have input.

This results in TicksetSerializer's assert failing, because there's an active tick past the last set one.

Instead, RewindableAction now serializes the last set tick, even if it was not set in the current loop. TicksetSerializer will not serialize ticks outside of the specified range.

Fixes #532