csg_inverse: better error message if step is incomplete
csg_inverse: better error message if step is incomplete

MrTheodor/csg,junghans/csg,MrTheodor/csg,votca/csg,junghans/csg,MrTheodor/csg,junghans/csg,junghans/csg,votca/csg,junghans/csg,junghans/csg,MrTheodor/csg,votca/csg,MrTheodor/csg,votca/csg