Don't bother to optimize the wall print order when there are no holes in the part.
Don't bother to optimize the wall print order when there are no holes in the part.

The original wall printing code now aligns the z-seams of the inner walls with the outer
wall so using the optimizing code is no longer beneficial.

Also, this change fixes a feature of the optimizing code that would cause the z-seams not
to be aligned in the specific situation where infill was being printed before walls, the
inner walls were printed before the outer and the part had no holes!

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