Also fixed the polygon start points when the z seam type is RANDOM.
Also fixed the polygon start points when the z seam type is RANDOM.

Using random start points make no sense at all if the wall printing order has been optimized.
I'm not sure it makes a lot of sense even when the wall printing order isn't optimized!

Anyway, it now orders the polygons based on the distances of the random start points from
the initial point rather than the distances of the points that are closest to the initial point.

Ultimaker/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,ROBO3D/CuraEngine,alephobjects/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine,ROBO3D/CuraEngine