alac enc: "channel layout change is not supported" with mono file

[ami_stuff]

this does not happen with "-acodec wavpack" or "-acodec flac"

​https://trac.ffmpeg.org/raw-attachment/ticket/10547/20_bit_fixed_96k_mono.osq

./ffmpeg -i 20_bit_fixed_96k_mono.osq -y -acodec alac out.mkv
ffmpeg version N-112164-gcb26b85953 Copyright (c) 2000-2023 the FFmpeg developers
  built with gcc 11 (Ubuntu 11.4.0-1ubuntu1~22.04)
  configuration: 
  libavutil      58. 25.100 / 58. 25.100
  libavcodec     60. 27.100 / 60. 27.100
  libavformat    60. 13.100 / 60. 13.100
  libavdevice    60.  2.101 / 60.  2.101
  libavfilter     9. 11.100 /  9. 11.100
  libswscale      7.  3.100 /  7.  3.100
  libswresample   4. 11.100 /  4. 11.100
[aist#0:0/osq @ 0x55d744704bc0] Guessed Channel Layout: mono
Input #0, osq, from '20_bit_fixed_96k_mono.osq':
  Duration: 00:00:06.76, start: 0.000000, bitrate: 1617 kb/s
  Stream #0:0: Audio: osq, 96000 Hz, 1 channels, s32p (20 bit)
Stream mapping:
  Stream #0:0 -> #0:0 (osq (native) -> alac (native))
Press [q] to stop, [?] for help
[Parsed_anull_0 @ 0x55d744707e00] Channel layout change is not supported
[af#0:0 @ 0x55d744703e40] Error while filtering: Not yet implemented in FFmpeg, patches welcome
Failed to inject frame into filter network: Not yet implemented in FFmpeg, patches welcome
Error while filtering: Not yet implemented in FFmpeg, patches welcome
[out#0/matroska @ 0x55d744705100] Nothing was written into output file, because at least one of its streams received no packets.
size=       0kB time=N/A bitrate=N/A speed=N/A    
Conversion failed!