Senemenelas Icy Caverns nothingness tile fix

Fix for the "empty nothingness" tile sic00_f01_01.mdl in Senemenelas' Icy Caverns; disables ambient/diffuse lighting on the boxes, so the green grid is no longer visible.

Note that this is only a single, extremely slightly modified model file. You'll still need the original tileset.

Install by placing in a hak at the top of your module's load order, with Senemenelas' Icy Caverns below it, so the modified .mdl can override the default one.