Investigate crash in newrat.m

See https://forum.dynare.org/t/mode-compute-5-in-dsge-var/10642 @rattoma Could you please have a look. The problem is that in the else-clause of

    if length(find(ig))<nx
        ggx=ggx*0;
        ggx(find(ig))=gg(find(ig));
        if analytic_derivation
            hhx=hh;
        else
            hhx = reshape(dum,nx,nx);
        end

the dum variable has not been set.