Fix bug when calling non-Bayesian smoother after Bayesian estimation

Because xparam1 is used by the smoother, but xparam was set to the posterior mean, the non-Bayesian smoother results were based on the parameters at the mode, which are stored in xparam1.

(cherry picked from commit 2c01113e8c3a40d8b134939ced740a39c74b4e5d)