Rounding errors could push us slightly outside the [-1, 1] range, which
caused acos() to return NaN, which in turn broke p2d_is_cw, and eventually
tripped create_interior_skeleton_and_offset_polygons_with_holes_2.
This broke p2d_is_cw which in turn tripped
CGAL::create_interior_skeleton_and_offset_polygons_with_holes_2
with the infamous
terminate called after throwing an instance of 'CGAL::Assertion_exception'
what(): CGAL ERROR: assertion violation!
Expr: lParent
File: /usr/include/CGAL/arrange_offset_polygons_2.h
Line: 94
