add missing variable checks in various places

src/lib/builtins.pl

@@ -261,7 +261,8 @@ call_or_cut(M:G, B) :-
     ;  call(M:G)
     ).
 call_or_cut(G, B) :-
-    (  '$call_with_default_policy'(control_functor(G)) ->
+    (  nonvar(G),
+       '$call_with_default_policy'(control_functor(G)) ->
        '$call_with_default_policy'(call_or_cut_interp(G, B))
     ;  call(G)
     ).

src/loader.pl

@@ -440,7 +440,8 @@ predicate_property(Callable, Property) :-
     ;  functor(Callable, (:), 2),
        arg(1, Callable, Module),
        arg(2, Callable, Callable0),
-       atom(Module) ->
+       atom(Module),
+       nonvar(Callable0) ->
        functor(Callable0, Name, Arity),
        (  atom(Name),
           Name \== [] ->