libstdc++: Fix-self element self-assigments when inserting an empty range [PR121313]

libstdc++: Fix-self element self-assigments when inserting an empty range [PR121313]

For __n == 0, the elements were self move-assigned by
std::move_backward(__ins, __old_finish - __n, __old_finish).

	PR libstdc++/121313

libstdc++-v3/ChangeLog:

	* include/bits/vector.tcc (vector::insert_range): Add check for
	empty size.
	* testsuite/23_containers/vector/modifiers/insert/insert_range.cc:
	New tests.

(cherry picked from commit cc54f2f47e63c9d404a44f618cf114ae63e81b40)