The crash was caused by an overflow in the opgl_path_segment_storage
array. It happened because shadow catcher paths would write to the
segments but not clear them. This made it so the next render loop
iteration for the main path starts with non-empty segments in the
guiding data.
Disable training when megakernel is called for the shadow catcher
state.
To ensure this issue is not forgotten when the guiding is ported to
GPU add asserts in the `guiding.h`. While it is a no-op for default
GPU kernels sometimes we do compile debug kernels. But also it acts
as a plain-text reminder to the future-us in working on the code.
There is now also an assert before the main path megakernel to help
catching such cases in the future.
Pull Request: https://projects.blender.org/blender/blender/pulls/137291
9f999adfc6