[Bug libstdc++/98001] ext/stdio_filebuf/char/79820.cc is broken

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98001

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I added b.close() before the fclose anyway. I'll backport this.