message: UI-QT: Minor bugfix for for isosurfaces of some 3D systems.
  If a system has no translations of the basis cell, it can still be 3D and the isosurfaces should be drawn. This was prevented by an incorrect usage of n_cell_step, which regulates the resolution of basis cells.
diff: @@ -392,7 +392,7 @@ void SpinWidget::updateVectorFieldGeometry()
  // get tetrahedra
  if (Geometry_Get_Dimensionality(state.get()) == 3)
  {
  - if (n_cells[0]/n_cell_step < 2 || n_cells[1]/n_cell_step < 2 || n_cells[2]/n_cell_step < 2)
  + if( n_cell_step > 1 && n_cells[0]/n_cell_step < 2 || n_cells[1]/n_cell_step < 2 || n_cells[2]/n_cell_step < 2 )
  {
  geometry = VFRendering::Geometry(positions, {}, {}, true);
  }
  