simplify: Fix border vs seam classification
simplify: Fix border vs seam classification

Our logic for checking if the vertex is a border or seam relied on the
vertex being the original one; if remap[i] != i, the logic breaks down
and can classify a seam vertex as a border, or a locked vertex as
seam/border.

Fix this by copying existing classification for remapped vertices.

zeux/meshoptimizer,zeux/meshoptimizer,zeux/meshoptimizer