fix cal_chi2 for 2D
fix cal_chi2 for 2D

lewisodriscoll/sasview,lewisodriscoll/sasview,SasView/sasview,SasView/sasview,SasView/sasview,lewisodriscoll/sasview,SasView/sasview,lewisodriscoll/sasview,SasView/sasview,SasView/sasview,lewisodriscoll/sasview