EMI: Allow actors to be hidden by a call to set_wear_chore(nil).

In EMI, actors are hidden by a call to set_wear_chore(nil). An early example of this is when Guybrush eats the pretzels in the SCUMM bar. It appears that the original engine stops the actor's wearChore as well when StopActorChores() is called, but ResidualVM wasn't doing that.

This code adds a new private variable to keep track of whether the wearChore is visible. When the wearChore is not visible, the draw() command is bypassed.