[PATCH] Fix libstdc++/8347

[B. Kosnik]

>Ok?

looks good...

>2002-10-25  Paolo Carlini  <pcarlini@unitus.it>
>
>        PR libstdc++/8347
>        * include/bits/basic_string.tcc
>        (string::_S_construct(_InIter, _InIter, const _Alloc&,
>        forward_iterator_tag)): Do not throw logic error if
>        __beg == NULL && __end == __beg.
>        (string::string(const _CharT*, const _Alloc&)): Tweak.
>        * testsuite/21_strings/ctor_copy_dtor.cc: Add test05 from PR.