Workbench doesn't fill all texture slots. In OpenGL it should match what
the shader is using, where some texture slots that have been defined can
be optimized away when not used. The Vulkan backend however uses all the
resources that has been defined in the shader create info.
When using a texture shader in workbench the shader would raise a
validation warning as there are slots defined that are never uploaded.
This PR fixes this by always set dummy textures in those slots.
Pull Request: https://projects.blender.org/blender/blender/pulls/127064
835e626a28