[Bug libstdc++/121154] Incorrect output of format(loc, "{:L}", x) for invalid month/weekday and loc not classic.

[tkaminsk at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121154

--- Comment #1 from Tomasz Kamiński <tkaminsk at gcc dot gnu.org> ---
This is the result of changes in r16-2251-gb2b7276a7e114d, when we call
_M_locale_fmt for invalid month/weekday, even if _M_debug is set.