[Bug libstdc++/81857] istreambuf_iterator not work as input iterator

[abominable-snowman at yandex dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81857

--- Comment #2 from Petr Ovtchenkov <abominable-snowman at yandex dot ru> ---
Related problem: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50119,
commit 1a1dad283 in git's reflection.