libstdc++: Fix vector(from_range_t, R&&) for exceptions [PR120367]

libstdc++: Fix vector(from_range_t, R&&) for exceptions [PR120367]

Because this constructor delegates to vector(a) the object has been
fully constructed and the destructor will run if an exception happens.
That means we need to set _M_finish == _M_start so that the destructor
doesn't try to destroy any elements.

libstdc++-v3/ChangeLog:

	PR libstdc++/120367
	* include/bits/stl_vector.h (_M_range_initialize): Initialize
	_M_impl._M_finish.
	* testsuite/23_containers/vector/cons/from_range.cc: Check with
	a type that throws on construction.
	exceptions during construction.

Reviewed-by: Patrick Palka <ppalka@redhat.com>