another correction linked to cova_compute

git-svn-id: https://www.dynare.org/svn/dynare/trunk@2408 ac1d8469-bf42-47a9-8791-bf33cf982152

matlab/dynare_estimation_1.m

@@ -524,6 +524,8 @@ if options_.mode_compute > 0 & options_.posterior_mode_estimation
                 else
                     hh = reshape(hessian('DsgeVarLikelihood',xparam1,options_.gstep,gend),nx,nx);
                 end
+            else
+                nn = repmat(NaN,length(xparam1),length(xparam1))
             end
         end
         if options_.cova_compute