Bugfix for simult_.m when used with k_order_pert and pruning at order=1

In the rare combination of k_order_solver, pruning, and order=1 the steady state was not subtracted from the starting values when doing simulations
Merge pull request #394 from JohannesPfeifer/k_order_pert_pruning_simult

Bugfix for simult_.m when used with k_order_pert and pruning at order=1