weird manifold id settings when converting to simplices

[drwells]

I saw this when looking closely at #13035:

This should be a cylinder, but it isn't (the top left and bottom right are wrong). It looks like we are not setting two line manifold ids correctly. Here is the code:

#include <deal.II/grid/grid_generator.h>
#include <deal.II/grid/grid_out.h>
#include <deal.II/grid/tria.h>

#include <fstream>

template <int dim> void check()
{
  using namespace dealii;
  Triangulation<dim> triangulation;

  {
    Triangulation<dim> x;
    GridGenerator::subdivided_cylinder(x, 4, 1, 2);

    GridGenerator::convert_hypercube_to_simplex_mesh(x, triangulation);
    for (const auto i : x.get_manifold_ids())
      if (i != numbers::flat_manifold_id)
        triangulation.set_manifold(i, x.get_manifold(i));
    triangulation.refine_global(3);
  }

  {
    GridOut go;
    std::ofstream out("out.vtk");
    go.write_vtk(triangulation, out);
  }
}

int main() { check<3>(); }

[bangerth]

Ah yes, good eyes!