check_POLYLINE_handles (Dwg_Object *obj)
{
  /* We ensured the common fields structure is shared with all 4 types */
  Dwg_Entity_POLYLINE_2D *_obj = obj->tio.entity->tio.POLYLINE_2D;
  Dwg_Data *dwg = obj->parent;

  if (dwg->header.version >= R_2004)
    {
      BITCODE_BL i = 0;
      Dwg_Object_Ref *layer = obj->tio.entity->layer;
      Dwg_Object_Ref *seqend = _obj->seqend;

      // resolve prev. object
      if (layer && !layer->obj)
        layer->obj = dwg_ref_object_relative (dwg, layer, obj);
      if (!layer || !layer->obj)
        { // maybe a reactor pointing forwards or vertex
          LOG_WARN ("Wrong POLYLINE.layer %lX",
                    layer ? layer->handleref.value : 0L);
          if (_obj->num_owned > 0 && _obj->vertex)
            {
              Dwg_Object_Ref *vertex = _obj->vertex[0];
              if (vertex && !vertex->obj)
                vertex->obj = dwg_ref_object_relative (dwg, vertex, obj);
              if (vertex && vertex->obj /* pointing backwards */
                  && vertex->obj->fixedtype == DWG_TYPE_LAYER)
                {
                  Dwg_Object *seq;
                  obj->tio.entity->layer = layer = vertex;
                  LOG_WARN (
                      "POLYLINE.layer is vertex[0] %lX, shift em, NULL seqend",
                      layer->handleref.value);
                  /* shift vertices one back */
                  for (i = 0; i < _obj->num_owned - 1; i++)
                    {
                      _obj->vertex[i] = _obj->vertex[i + 1];
                    }
                  _obj->vertex[_obj->num_owned - 1] = seqend;
                  _obj->seqend = NULL;
                  /* now just seqend is empty.
                     either 1+ last_vertex, or one before the first.
                     Here the next object might not be read yet. */
                  seq = dwg_next_object (obj);
                  if (seq && seq->type == DWG_TYPE_SEQEND)
                    {
                      LOG_WARN ("POLYLINE.seqend = POLYLINE+1 %lX",
                                seq->handle.value);
                      seqend = _obj->seqend = dwg_find_objectref (dwg, seq);
                    }
                  else
                    {
                      seq = dwg_next_object (seqend->obj);
                      if (seq && seq->type == DWG_TYPE_SEQEND)
                        {
                          LOG_WARN ("POLYLINE.seqend = VERTEX+1 %lX",
                                    seq->handle.value);
                          seqend = _obj->seqend
                              = dwg_find_objectref (dwg, seq);
                        }
                    }
                }
            }
        }
      else if (layer->obj->fixedtype != DWG_TYPE_LAYER
               && layer->obj->fixedtype != DWG_TYPE_DICTIONARY)
        { // a vertex would be after, a reactor before
          LOG_WARN ("Wrong POLYLINE.layer %s", layer->obj->dxfname)
        }
      // a SEQEND is always after the polyline, so it cannot be resolved yet
      if (!seqend || !seqend->handleref.value)
        {
          LOG_WARN ("Empty POLYLINE.seqend")
        }
      else if (seqend->obj && seqend->obj->fixedtype != DWG_TYPE_SEQEND)
        { // most likely a vertex, off by one
          LOG_WARN ("Wrong POLYLINE.seqend %s", seqend->obj->dxfname)
        }
      if (!_obj->vertex)
        return;
      for (; i < _obj->num_owned; i++)
        {
          Dwg_Object_Ref *v = _obj->vertex[i];
          if (!v || !v->handleref.value)
            {
              LOG_WARN ("Empty POLYLINE.vertex[%d]", i);
            }
          else if (v->obj && v->obj->fixedtype != DWG_TYPE_VERTEX_2D
                   && v->obj->fixedtype != DWG_TYPE_VERTEX_3D
                   && v->obj->fixedtype != DWG_TYPE_VERTEX_MESH
                   && v->obj->fixedtype != DWG_TYPE_VERTEX_PFACE
                   && v->obj->fixedtype != DWG_TYPE_VERTEX_PFACE_FACE)
            {
              LOG_WARN ("Wrong POLYLINE.vertex[%d] %lX %s", i,
                        v->handleref.value, v->obj->dxfname)
            }
        }
    }
}