`sd->type` was set to `PRIMITIVE_TRIANGLE` when it should be
`PRIMITIVE_LAMP`.
Function #lights_intersect_impl sets `isect->prim` to `lamp`, which is
passed to function #shader_setup_from_sample. There `prim != PRIM_NONE`
is evaluated to `true`, thus setting `sd->type` to `PRIMITIVE_TRIANGLE`
erroneously. This fix checks `lamp != LAMP_NONE` first, as in all other
usages of #shader_setup_from_sample `LAMP_NONE` is passed as the value
of `lamp`.
Pull Request: https://projects.blender.org/blender/blender/pulls/108769
84863dae89