It seems for very narrow tall paths it is possible for the dxdy value
to round to a value (that after many repeated additions) overshoots
the desired end x. This caused a (rather rare) crash on this 3D canvas
demo: https://www.kevs3d.co.uk/dev/html5logo/. For now, lets just avoid
a crash here. This does not make any noticeable visual differences on
the demos I tired.