The issue was an out-of-bounds read access when checking whether
the world volume emission needs to be accumulated.
Solution is to check for this case. Done in the generic place, so
that the shade_volume kernel is more readable and no branching
added there, and there is no impact on scenes without the light
linking.
Assume that the world emissive volume belongs to the default light
linking group, as there is no way to link it explicitly to anything.
Pull Request: https://projects.blender.org/blender/blender/pulls/110733
8ea68765fc