functions.h (__foreign_iterator_aux3(const _Safe_iterator<>&, const _InputeIter&, const _InputIter&, __true_type)): Use empty() rather than begin() == end().

2018-09-28  François Dumont  <fdumont@gcc.gnu.org>

	* include/debug/functions.h
	(__foreign_iterator_aux3(const _Safe_iterator<>&, const _InputeIter&,
	const _InputIter&, __true_type)): Use empty() rather than begin() ==
	end().

From-SVN: r264699