In Cycles lights can be given a light falloff node to control their
light falloff.
This worked by multiplying the light's strength by different
combinations of the ray length, which would be FLT_MAX for
distant lights. This resulting in almost every configuration of the
light falloff node overflowing when used on distant lights, which is
undesirable.
This commit fixes this issue by ignoring most of the functions of the
light falloff node when used on a distant light.
And in the process fixes a small discrepancy between SVM and OSL when
using the light falloff node on distant lights.
Pull Request: https://projects.blender.org/blender/blender/pulls/134539
bcec81c4be