Consider range of value-initialized iterators as valid and empty.
libstdc++-v3/ChangeLog:
PR libstdc++/114316
* include/debug/safe_iterator.tcc (_Safe_iterator<>::_M_valid_range):
First check if both iterators are value-initialized before checking if
singular.
* testsuite/23_containers/set/debug/114316.cc: New test case.
* testsuite/23_containers/vector/debug/114316.cc: New test case.