There were two issues:
* The `new_point_counts_per_curve` was one too large, resulting in
`interpolate_from_neighbors` reading invalid memory.
* Writing the counts into the existing offsets array didn't quite work
because there can be a collision at the offset right between the
last old curve and the first new point. There was a race condition
where this value could be read and written at the same time.
Jacques Lucke
6899474615