Fix steady_state_model-block check with instruments
I have a model with
steady_state_model; Q=1/R; end; planner_objective Welfare; ramsey_model(instruments=(R),planner_discount=betta);
This is a proper conditional steady state file, where the instrument is taken as given. But it results in
ERROR: in the 'steady_state_model' block, variable 'R' is undefined in the declaration of variable 'Q'
because the preprocessor check does not account for the conditionality.