libstdc++: Fix access issue in elements_view::_Sentinel [PR100631]

In the earlier commit r12-854 I forgot to also rewrite the other operator-
overload in terms of the split-out member function _M_distance_from.

libstdc++-v3/ChangeLog:

	PR libstdc++/100631
	* include/std/ranges (elements_view::_Sentinel::operator-): Use
	_M_distance_from in the other operator- overload too.
	* testsuite/std/ranges/adaptors/elements.cc (test06): Augment test.