Caused by a subtle logic change in 17d161f565 and follow ups.
Because they used to be stored in a singly-linked list, the old storage
for `corners_by_space` was backwards compared to the order each corner
was discovered in `split_loop_nor_fan_do`. I don't fully understand how
yet, but the logic when setting edges sharp based on divergence between
neighboring corner normals in a space relied on the iteration direction,
so as a fix, just iterate backwards over the corners in each space.
7449f0e14c