a46def32b4
The material index in Grease Pencil attributes can be negative, since they are a generic attribute. The shader, however, requires clamping of the material index to avoid an invalid lookup. This was already happening for the material buffer setup (`grease_pencil_object_cache_populate`), but not for the actual VBO. Fixes #131670 Pull Request: https://projects.blender.org/blender/blender/pulls/132804