Fix part of #33662: cycles crash using displacement on meshes with vertices not attached to any face.
Fix part of #33662: cycles crash using displacement on meshes with vertices not
attached to any face.

tangent-opensource/coreBlackbird,pyrochlore/cycles,pyrochlore/cycles,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,pyrochlore/cycles