Small gears with too large backlash cause CGAL assertion errors

[hyperair]

The following causes CGAL assertions as per openscad/openscad#791.

use <MCAD/involute_gears.scad>

function convert_circular_pitch (circular_pitch) = circular_pitch * 180 / PI;

gear (
    circular_pitch = convert_circular_pitch (3),
    number_of_teeth = 8,
    backlash = 0.4,
    clearance = 0.4,
    bore_diameter = 0,
    rim_width = 999,
    rim_thickness = 10,
    gear_thickness = 10,
    hub_thickness = 10,
    hub_diameter = 0);

This appears to be caused by two points of the thinnest involute_gear_tooth polygon being inverted, possibly due to a rounding error.

[hyperair]

Reducing the backlash fixes the issue, but I think that it would be better to avoid having that triangle altogether.