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. disp_dr and th_autocovariances, because they are looking for dr.ghs2 which would be there at order=2