Fills the slot setting the count as the max stacking value of the item.
Slot slot = Slot(new Item.Snowball(), 1); assert(slot.count == 1); slot.fill(); assert(slot.count == 16);
Like full, this function requires item to not be null due to its call on its max property.
if(slot.item !is null) { slot.fill(); }
See Implementation
Fills the slot setting the count as the max stacking value of the item.