Fix issue with purely forward deterministic models with lags on exogenous.

Ref #617

(cherry picked from commit 6e0d9197)

matlab/sim1_purely_forward.m

@@ -39,7 +39,7 @@ function sim1_purely_forward()
                              1, 1, options_.gstep, options_.solve_tolf, ...
                              options_.solve_tolx, options_.simul.maxit, ...
                              options_.debug,oo_.exo_simul, M_.params, oo_.steady_state, ...
-                             it);
+                             it+M_.maximum_lag);
 
         if info
             skipline(2);