[BUG] `linear_sweep` cannot produce geometry with exactly N + 1/2 rotations

[bracketttc]

Describe the bug

linear_sweep cannot produce geometry with exactly N + 1/2 rotations.

Code To Reproduce Bug

region = regular_ngon( 6, 8 );
linear_sweep( region, height=100, twist=180);

ERROR: Assertion '(norm(v) >= _EPSILON)' failed: "
Cannot normalize a zero vector." in file /usr/share/openscad/libraries/BOSL2/vectors.scad, line 227
TRACE: called by 'unit' infile /usr/share/openscad/libraries/BOSL2/skin.scad, line 795
TRACE: called by '_make_all_prism_anchors' in file /usr/share/openscad/libraries/BOSL2/skin.scad, line 931
TRACE: called by 'linear_sweep' in file /usr/share/openscad/libraries/BOSL2/skin.scad, line 766
TRACE: caled by 'linear_sweep' in file poc.scad, line 3

Expected behavior
Produces solid with a hexagonal cross-section that sweeps around a half turn.

Screenshots
Not necessary.

Additional context
Add any other context about the problem here.

• OpenSCAD Version: 2.0.736 packaged by Fedora
• Other libraries used: