The simplify modifier uses `bke::curves_copy_point_selection` but didn't build the `points_to_keep` index mask correctly. This fixes the indices in the index mask and also optimizes the edge cases of removing all the points/ keeping all the points.
The simplify modifier uses `bke::curves_copy_point_selection` but didn't build the `points_to_keep` index mask correctly. This fixes the indices in the index mask and also optimizes the edge cases of removing all the points/ keeping all the points.