mtllib issue-140-zero-face-idx.mtl

v -0.5 -0.5 0
v 0.5 -0.5 0
v 0.5 0.5 0
v -0.5 0.5 0

vt 0 0 0
vt 1 0 0
vt 1 1 0
vt 0 1 0

vn 0 0 -1

usemtl main
f 0/0/0 1/1/0 3/3/0
f 1/1/0 3/3/0 2/2/0