Reported by Ian Shumsky:

1) Export STL from fn_bug.scad
   - fn_setting = 41 -> triggers bug
   - fn_setting = 40 -> works

2) Open fn_bug_import.scad and render using CGAL (F6)

->
CGAL error in CGA_Nef_polyhedron3(): CGAL ERROR: assertion violation!
Expr: pe_prev->is_border() || !internal::Plane_constructor<Plane>::get_plane(pe_prev->facet(),pe_prev->facet()->plane()).is_degenerate()
File: ../libraries/install/include/CGAL/Nef_3/polyhedron_3_to_nef_3.h
Line: 252