message: gltfpack: Guard against empty meshes in optimizeMesh/simplifyMesh
  Both functions technically worked, but optimizeMesh would cause an
  assertion in STL debug runtimes (MSVC/Debug or libstdc++/_GLIBCXX_DEBUG).
  Fixes
diff: @@ -533,6 +533,9 @@ static void simplifyMesh(Mesh& mesh, float threshold, bool aggressive)
  {
  assert(mesh.type == cgltf_primitive_type_triangles);
  + if (mesh.indices.empty())
  + return;
  +
  const Stream* positions = getStream(mesh, cgltf_attribute_type_position);
  if (!positions)
  return;
  @@ -565,6 +568,9 @@ static void optimizeMesh(Mesh& mesh, bool compressmore)
  {
  assert(mesh.type == cgltf_primitive_type_triangles);
  + if (mesh.indices.empty())
  + return;
  +
  size_t vertex_count = mesh.streams[0].data.size();
  if (compressmore)
  