Fixed a bug, where the top or bottom solid layers were created even if the number of top / bottom solid layers was set to zero while the top / bottom minimum shell thickess was set nonzero.
Fixed a bug, where the top or bottom solid layers were created even
if the number of top / bottom solid layers was set to zero while
the top / bottom minimum shell thickess was set nonzero.

With this commit, if the top / bottom solid layers is set to zero,
there are no top / bottom solid layers generated independent from
the minimum top / bottom shell thickness.

prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r