moments_varendo: compute variance decomposition only if there is more than one exogenous variable

matlab/compute_moments_varendo.m

@@ -94,6 +94,7 @@ else
     end
 end
 % VARIANCE DECOMPOSITION.
+if M_.exo_nbr > 1
     if posterior
         for i=1:NumberOfEndogenousVariables
             for j=1:NumberOfExogenousVariables
@@ -123,3 +124,4 @@ if Steps
             end
         end
     end
+end