[Bug libstdc++/81122] parsing f stopped after '0' when reading std::hexfloat >> f;

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81122

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is probably caused by https://wg21.link/lwg2381