I am trying to apply `Delaunay_mesher_2::refine_mesh` to a set of numbered vertices (i.e. vertex class is `Triangulation_vertex_base_with_id_2`). I expect that any vertex created in the process should have `id()==0`. However it turns out to be not the case. Instead, the IDs have various positive/negative values.

I tried using `Triangulation_vertex_base_with_info_2`, but the result was the same.

More or less my code works like this:

```cpp
using K = CGAL::Exact_predicates_inexact_constructions_kernel;
using Vb = CGAL::Triangulation_vertex_base_with_id_2<K>;
using Fb = CGAL::Delaunay_mesh_face_base_2<K>;
using Tds = CGAL::Triangulation_data_structure_2<Vb, Fb>;
using CDT_Tag = CGAL::Exact_intersections_tag;
using CDT = CGAL::Constrained_Delaunay_triangulation_2<K, Tds, CDT_Tag>;
using Criteria = CGAL::Delaunay_mesh_size_criteria_2<CDT>;
CDT cdt;
CGAL::Delaunay_mesher_2<CDT, Criteria> mesher(cdt, Criteria(0.125, 0.5));
... // Add some points and constraints.
static const CDT::Point INFINITE_POINT = { 1e100, 1e100 };
std::vector<CDT::Point> seeds = { INFINITE_POINT };
mesher.set_seeds(seeds.begin(), seeds.end());
mesher.refine_mesh();

for (auto vertices_iter = cdt.finite_vertices_begin();
     vertices_iter != cdt.finite_vertices_end();
     ++vertices_iter) {
  // do something with vertices_iter->id().
}

```