Fix bug introduced in issue 1336
In 7829a252 related to https://github.com/DynareTeam/dynare/issues/1336 we set
order=1 locally in
stochastic_solvers. While that speeds up the solution, the subsequent functions do not know that
order was locally changed. That crashes e.g.
th_autocovariances, because they are looking for
dr.ghs2 which would be there at