Fix bug in MakeCylinder2d when angles are close

[jkozdon]

Ran into a problem with MakeCylinder2d when the angles were different signs but still close enough together (one of the angles was close to zero, but had the opposite sign and adding 2*pi too it to a reflex angle). I think that really you want to check that the distance between the angles is less than pi and not worry about the sign difference. (I don't think that the while loop will evaluate true more than once and so could be replaced with an if statement.)