[Bug libstdc++/65049] Undefined behaviour with std::char_traits<char>

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65049

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, unfortunately the C++ standard doesn't define those members in terms of
the C library calls they correspond to, and doesn't say anything special about
null pointers, so they're required to handle null (I'm considering whether that
could be considered a defect, we might want to forbid nulls so I'll raise that
with the committee).