Anonymous variables cause unsafe errors

[jinulee-v]

Hi there,

There is a bug regarding anonymous variables.
Considering the program

a(X) :- b(X, _).
b(x, y).
b(z, w).

This internally translates to

_xclingo_sup(1,a(X),(b(X,_),)):-[#inc_base];_xclingo_model(b(X,_)).

which is then annotated by clingo as

_xclingo_sup(1,a(X),(b(X,#Anon0),)):-[#inc_base];_xclingo_model(b(X,#Anon1)).

, making #Anon0 unsafe.
However, naming this variable (e.g. a(X) :- b(X, Y).) does not raise this error.