Fix #143333: Custom bone shape does not include subdivision surface

This was caused by a mismatch in the conditions that enabled GPU
subdivision. The mesh normals domain for meshes with no faces was
reported incorrectly, causing the code to think there are auto-smooth
style split normals when there actually aren't.

Also the GPU subdiv normals extraction had a crash binding a vertex
buffer that doesn't exist when there are no faces. Add an early return
for the wire-only mesh case to avoid that.

Pull Request: https://projects.blender.org/blender/blender/pulls/143961

source/blender/blenkernel/intern/mesh_normals.cc

@@ -294,6 +294,10 @@ blender::bke::MeshNormalDomain Mesh::normals_domain(const bool support_sharp_fac
 {
   using namespace blender;
   using namespace blender::bke;
+  if (this->faces_num == 0) {
+    return MeshNormalDomain::Point;
+  }
+
   const bke::AttributeAccessor attributes = this->attributes();
   if (const std::optional<AttributeMetaData> custom = attributes.lookup_meta_data("custom_normal"))
   {

source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_lnor.cc

@@ -315,6 +315,10 @@ gpu::VertBufPtr extract_normals_subdiv(const MeshRenderData &mr,
 
   gpu::VertBufPtr lnor = gpu::VertBufPtr(
       GPU_vertbuf_create_on_device(get_normals_format(), vbo_size));
+  if (subdiv_cache.num_subdiv_loops == 0) {
+    update_loose_normals(mr, subdiv_cache, *lnor);
+    return lnor;
+  }
 
   if (subdiv_cache.use_custom_loop_normals) {
     const Mesh *coarse_mesh = subdiv_cache.mesh;