An output iterator passed as the unused first argument to __niter_wrap
might have already been invalidated, so don't copy it.

	PR libstdc++/86658
	* include/bits/stl_algobase.h (__niter_wrap<_Iterator>): Pass unused
	parameter by reference, to avoid copying invalid iterators.
	* testsuite/25_algorithms/copy/86658.cc: New test.

From-SVN: r262952