Set default width to no larger than inventorySize
Add allowDrop option (on by default) to enable/disable 'writing' to an inventory
Add allowPickup option to enable/disable picking up items (on by default)

Could be useful to allow an item for display purposes only (if also
disabled allowDrop), or for inventories you can give to but never take.
Because giving is better than receiving right?
Allow merging into held pile when left-clicking pickup-only (no drop) inventory

Normally left-click drops the pile, but since the inventory doesn't allow it,
merge the inventory pile into the held pile instead. Allows for convenient crafting
in voxel-inventory-dialog (repeatedly click result inventory to continue to craft).
Fix undefined deref when clicking on empty no-drop inventory, attempting to merge nonexistent pile