Check during MF::reinit() if AffineConstraints are closed

[peterrum]

If one does not close, the following MatrixFree object gives different results, depending on fast HN algorithm is enabled or not:

  Triangulation<dim> tria;
  GridGenerator::subdivided_hyper_cube(tria, 2);
  tria.begin()->set_refine_flag();
  tria.execute_coarsening_and_refinement();

  QGauss<dim>    quad(degree + 1);
  FE_Q<dim>      fe(degree);
  MappingQ1<dim> mapping;

  DoFHandler<dim> dof_handler;
  dof_handler.reinit(tria);
  dof_handler.distribute_dofs(fe);

  AffineConstraints<Number> constraints;
  DoFTools::make_zero_boundary_constraints(dof_handler, constraints);
  DoFTools::make_hanging_node_constraints(dof_handler, constraints);
  constraints.close(); // needed!!!

  typename MatrixFree<dim, Number, VectorizedArrayType>::AdditionalData
    additional_data;
  additional_data.mapping_update_flags = update_values | update_gradients |
                                         update_JxW_values |
                                         dealii::update_quadrature_points;

  MatrixFree<dim, Number, VectorizedArrayType> matrix_free;
  matrix_free.reinit(mapping, dof_handler, constraints, quad, additional_data);

depends on #13505

[peterrum]

/rebuild

[peterrum]

I have rebased this PR!