Move checking an explicit VARIADIC "any" argument into the parser.

This is more efficient and simpler . It does mean that an untyped NULL
can no longer be used in such cases, which should be mentioned in
Release Notes, but doesn't seem a terrible loss. The workaround is to
cast the NULL to some array type.

Pavel Stehule, reviewed by Jeevan Chalke.

src/backend/catalog/pg_aggregate.c

@@ -332,6 +332,7 @@ lookup_agg_function(List *fnName,
 	Oid			fnOid;
 	bool		retset;
 	int			nvargs;
+	Oid			vatype;
 	Oid		   *true_oid_array;
 	FuncDetailCode fdresult;
 	AclResult	aclresult;
@@ -346,7 +347,8 @@ lookup_agg_function(List *fnName,
 	 */
 	fdresult = func_get_detail(fnName, NIL, NIL,
 							   nargs, input_types, false, false,
-							   &fnOid, rettype, &retset, &nvargs,
+							   &fnOid, rettype, &retset,
+							   &nvargs, &vatype,
 							   &true_oid_array, NULL);
 
 	/* only valid case is a normal function not returning a set */