The reason for this to happen is because when spatial split is used
the same intersection could be recorded twice (via different BVH nodes).
This change introduces check for the intersection being already recoded,
similar to the check in the local BVH. The check is done during BVH
intersection which allows to properly ignore intersections even for the
maximum bounce number check. A faster approach would be to do such
filtering after sorting, but then we can not keep bounce check in the
BVH code consistent with and without spatial splits.
Intuitively it seems that it should be possible to merge the new loop
with the one that checks for which intersection to keep. But it is not
so trivial in practice: it doesn't run for all intersections, and also
it is formulated in a way that updates isect_index for the next record.
Pull Request: https://projects.blender.org/blender/blender/pulls/136251
50180283e9