[Bug libstdc++/91653] ostream::operator<<(streambuf*) should fail the ostream when write output stream error but not

[yhliang86 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91653

--- Comment #2 from yinghui <yhliang86 at hotmail dot com> ---
(In reply to Jonathan Wakely from comment #1)
> GCC 4.9.2 has been unsupported for several years.

but both the code and the problem still keeps exactly the same.

I have seen many c++ code write 'os << is.rdbuf()` as a stream copy idiom, and
this may silently write corrupted data in case like disk full.