The function `recursive_build()` can change the `shared_ptr` by making
it an internal node. If `root_` is modified, it could happen that when
the children are accessing `root_->bbox.min` that memory is already
freed.
Storing `bbox_min` separately seems to fix the issue. No error is seen
after running the tests repeatedly for 2000 times.
Pull Request: https://projects.blender.org/blender/blender/pulls/145239
3bbce15497