fix #951 fixed NaN values, moved segment density from array value to attribute
fix #951 fixed NaN values, moved segment density from array value to attribute

mrakitin/sirepo,mkeilman/sirepo,mkeilman/sirepo,radiasoft/sirepo,mrakitin/sirepo,radiasoft/sirepo,mrakitin/sirepo,radiasoft/sirepo,mkeilman/sirepo,radiasoft/sirepo,mrakitin/sirepo,mkeilman/sirepo,radiasoft/sirepo