[Bug libstdc++/95322] std::list | take | transform, expression does not work cbegin() == end()

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95322

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
There's an implicit conversion from sentinel<false> to sentinel<true>, but that
would only happen if the operator== had been found, and since it's a hidden
friend it can't be found unless one of the operands is already sentinel<true>.