Initialize instr_id field of discretionary_policy

(cherry picked from commit dd0e9fe7)

matlab/global_initialization.m

@@ -117,6 +117,7 @@ M_.osr.param_bounds=[];
 M_.osr.variable_weights=[];
 M_.osr.variable_indices =[];
 
+M_.instr_id=[];
 % Set default options_ in function below; this change was made for the GUI
 options_ = default_option_values(M_);