Get the last object that used the placeable object that is calling this function.
Returns the last object that used the placeable or door object that is calling this function.
Returns OBJECT_INVALID if it is called by something other than a placeable or a door.
Pretty much the same function as GetLastOpenedBy but can be called from placeables that are not openable but are usable.
author: Jody Fletcher, editor: John Shuell