Hi,

I have a file which I can't down-mix to stereo due to
AV_CHANNEL_ORDER_NATIVE requirement in sane_layout.

```
$ ffmpeg -i COMMUNITY_HERO_2.mov -vn -af
'aformat=sample_rates=48000:channel_layouts=stereo' -y /tmp/out.wav
ffmpeg version N-118381-g4ba9ae7742 Copyright (c) 2000-2025 the FFmpeg
developers
  built with gcc 7 (SUSE Linux)
  configuration: --prefix=/Developer/x86_64 --prefix=/Developer/x86_64
--enable-runtime-cpudetect --enable-libzimg --enable-libx264
--enable-libass --enable-libmodplug --enable-libxml2 --enable-libvmaf
--enable-shared --enable-pthreads --enable-gpl --enable-version3
--enable-gnutls --enable-libfreetype --enable-pic --disable-static
--enable-shared --enable-rpath --enable-ffnvcodec --enable-debug
--disable-stripping --disable-optimizations --disable-mmx
  libavutil      59. 56.100 / 59. 56.100
  libavcodec     61. 31.101 / 61. 31.101
  libavformat    61.  9.106 / 61.  9.106
  libavdevice    61.  4.100 / 61.  4.100
  libavfilter    10.  9.100 / 10.  9.100
  libswscale      8. 13.100 /  8. 13.100
  libswresample   5.  4.100 /  5.  4.100
  libpostproc    58.  4.100 / 58.  4.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'COMMUNITY_HERO_2.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 512
    compatible_brands: qt
    encoder         : Lavf58.29.100
  Duration: 00:02:02.86, start: 0.000000, bitrate: 97805 kb/s
  Stream #0:0[0x1]: Video: prores (LT) (apcs / 0x73637061), yuv422p10le(top
first), 1920x1080, 88583 kb/s, SAR 1:1 DAR 16:9, 29.97 fps, 29.97 tbr, 30k
tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : FFMP
      encoder         : Lavc58.54.100 prores
      timecode        : 14:25:46;28
  Stream #0:1[0x2]: Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, 8
channels (FL+FR+FC+LFE+SL+SR+BL+BR), s32 (24 bit), 9216 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
  Stream #0:2[0x3](eng): Data: none (tmcd / 0x64636D74)
    Metadata:
      handler_name    : TimeCodeHandler
      timecode        : 14:25:46;28
Stream mapping:
  Stream #0:1 -> #0:0 (pcm_s24le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
[auto_aresample_0 @ 0x7ff5bc004900] [SWR @ 0x7ff5bc0049f0] Input channel
layout '8 channels (FL+FR+FC+LFE+SL+SR+BL+BR)' is not supported
[auto_aresample_0 @ 0x7ff5bc004900] Failed to configure output pad on
auto_aresample_0
[af#0:0 @ 0x21841830] Error reinitializing filters!
[af#0:0 @ 0x21841830] Task finished with error code: -22 (Invalid argument)
[af#0:0 @ 0x21841830] Terminating thread with return code -22 (Invalid
argument)
[aost#0:0/pcm_s16le @ 0x218412b0] [enc:pcm_s16le @ 0x21841770] Could not
open encoder before EOF
[aost#0:0/pcm_s16le @ 0x218412b0] Task finished with error code: -22
(Invalid argument)
[aost#0:0/pcm_s16le @ 0x218412b0] Terminating thread with return code -22
(Invalid argument)
[out#0/wav @ 0x21840b80] Nothing was written into output file, because at
least one of its streams received no packets.
size=       0KiB time=N/A bitrate=N/A speed=N/A
Conversion failed!
```

If I remove 2 lines from sane_layout then I am able to process this file
successfully.
However IDK the implications of this change.
In any case, I'm attaching the patch here, and hopefully someone more
knowledgeable can come up with a more appropriate fix.