The MT client crashes sometimes when trying to do a
lighting calc on upright_sprite entity visuals.
This may or may not be fixed in a future release, since it's
a heisenbug and a rare use-case, so for now try to
eliminate use of the rare and poorly supported upright_sprite
visual type by making empty inventory slots craftitem extrude
meshes.
As a limitation, for now, virtual_items such as injury or
lux burns will be invisible instead of showing the icon, as
we can't swap out the texture like we could for upright_sprite.
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