`num_distribution` in `KernelIntegrator` has type `int`, which holds a
maximal value of 2147483647. However, when computing the distribution,
`size_t` is used, which can go beyond this value and result in a
negative value when converted to `int`.
This PR handles this case as an error, stops rendering and suggests
alternative solutions.
Also early return when `use_light_tree`. The block was there because
`num_distribution` was needed for light tree before bfd1836861.
Pull Request: https://projects.blender.org/blender/blender/pulls/123177
e639c3d6e2