message: gltfpack: Avoid simplifying mesh to nothing
  With small meshes, the target index count can become zero; the
  simplifiers are happy to provide an empty mesh when asked for it, but we
  can't serialize an empty mesh.
diff: @@ -844,6 +844,9 @@ void simplifyMesh(Mesh& mesh, float threshold, bool aggressive)
  size_t target_index_count = size_t(double(mesh.indices.size() / 3) * threshold) * 3;
  float target_error = 1e-2f;
  + if (target_index_count < 1)
  + return;
  +
  std::vector<unsigned int> indices(mesh.indices.size());
  indices.resize(meshopt_simplify(&indices[0], &mesh.indices[0], mesh.indices.size(), positions->data[0].f, vertex_count, sizeof(Attr), target_index_count, target_error));
  mesh.indices.swap(indices);
  @@ -893,6 +896,9 @@ void simplifyPointMesh(Mesh& mesh, float threshold)
  size_t target_vertex_count = size_t(double(vertex_count) * threshold);
  + if (target_vertex_count < 1)
  + return;
  +
  std::vector<unsigned int> indices(target_vertex_count);
  indices.resize(meshopt_simplifyPoints(&indices[0], positions->data[0].f, vertex_count, sizeof(Attr), target_vertex_count));
  