trivial one- and zero-vertex polygons produce NaNs

[byorgey]

polygon (with & polyType .~ PolyRegular 1 1) :: [P2]

produces [P (NaN ^& NaN)]. Instead it ought to produce [P (1 ^& 0)].

Also, replacing PolyRegular 1 1 by PolyRegular 0 1 produces the same result. This is even more wrong; it ought to produce an empty list.

[byorgey]

Looking at this again, I am no longer convinced that PolyRegular 0 1 ought to produce an empty list; polygon is supposed to produce any TrailLike and there is not really any suitable way to have a TrailLike produce an empty list of points.