Add assertions to extract(const_iterator) functions

Add assertions to extract(const_iterator) functions

	* include/bits/stl_map.h (map::extract(const_iterator)): Assert that
	iterator is not past-the-end.
	* include/bits/stl_multimap.h (multimap::extract(const_iterator)):
	Likewise.
	* include/bits/stl_multiset.h (multiset::extract(const_iterator)):
	Likewise.
	* include/bits/stl_set.h (set::extract(const_iterator)): Likewise.
	* include/bits/unordered_map.h (unordered_map::extract(const_iterator))
	(unordered_multimap::extract(const_iterator)): Likewise.
	* include/bits/unordered_set.h (unordered_set::extract(const_iterator))
	(unordered_multiset::extract(const_iterator)): Likewise.

From-SVN: r240487