accented characters in FFREPORT variable create wrong log filename

[m.feriati]

Summary of the bug
this has been around for a long time, maybe years.
on windows, if the filename set in FFREPORT environment variable contains accented characters, the resulting log won't match the expected filename, although the log contains the correct filename.

ffplay started on 2024-10-11 at 16:22:37
Report written to "00 - hétérogénéisé.log"
Log level: 40
Command line:
gyan-lay -hide_banner -noborder -i "00 - h\xe9t\xe9rog\xe9n\xe9is\xe9.mp4" -vf "scale=1280:-2,setsar=1"
Initialized direct3d renderer.

also tried different console code pages with no success

chcp 1252
chcp 65001 :: my default console code page
chcp 437

expected behavior: produce 00 - hétérogénéisé.log
actual behavior: produces 00 - hétérogénéisé.log

hint
the target name can be recovered by reading the log filename bytes in code page 1252 and then rewritten as utf8

fyi
this applies to all ffmpeg binaries.

How to reproduce:

> set "FFREPORT=file=00 - hétérogénéisé.log:level=40"
> ffplay -hide_banner -noborder -i "in\00 - hétérogénéisé.mp4" -vf scale=1280:-2,setsar=1

>gyan-peg -version
ffmpeg started on 2024-10-11 at 16:15:29
Report written to "00 - hétérogénéisé.log"
Log level: 40
ffmpeg version 7.1-full_build-www.gyan.dev Copyright (c) 2000-2024 the FFmpeg developers