When drawing hair/curves the material shader has a "a" texture slot, but this slot was never bound to a texture. This PR fixes this by adding a default texture to it and when available tries to bind CD_AUTO_FROM_NAME resources. This part seems to be not implemented when the new curve rendering was added. `CD_AUTO_FROM_NAME` was never considered and therefore the layer could not be found and the sampler could not be found. Fixes #115460 Pull Request: https://projects.blender.org/blender/blender/pulls/121064