Changed mass check from == to <=0.0 to trigger error
Changed mass check from == to <=0.0 to trigger error

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