smc enc: artefacts in the output file 2

[ami_stuff]

​https://trac.ffmpeg.org/raw-attachment/ticket/10068/gold2.avi

./ffmpeg_g -i gold2.avi -s 557x333 -vcodec smc -y out.mov
ffmpeg version N-109332-g45ab5307a6 Copyright (c) 2000-2022 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.4.0-1ubuntu1~20.04.1)
  configuration: --enable-libopenjpeg
  libavutil      57. 43.100 / 57. 43.100
  libavcodec     59. 54.100 / 59. 54.100
  libavformat    59. 34.102 / 59. 34.102
  libavdevice    59.  8.101 / 59.  8.101
  libavfilter     8. 51.100 /  8. 51.100
  libswscale      6.  8.112 /  6.  8.112
  libswresample   4.  9.100 /  4.  9.100
Input #0, avi, from 'gold2.avi':
  Duration: 00:00:12.00, start: 0.000000, bitrate: 153 kb/s
  Stream #0:0: Video: srgc (srgc / 0x63677273), bgra, 299x171, 149 kb/s, 15 fps, 15 tbr, 15 tbn
Stream mapping:
  Stream #0:0 -> #0:0 (srgc (native) -> smc (native))
Press [q] to stop, [?] for help
Output #0, mov, to 'out.mov':
  Metadata:
    encoder         : Lavf59.34.102
  Stream #0:0: Video: smc (smc  / 0x20636D73), pal8(pc, progressive), 557x333, q=2-31, 200 kb/s, 15 fps, 15360 tbn
    Metadata:
      encoder         : Lavc59.54.100 smc
frame=    0 fps=0.0 q=-0.0 size=       0kB time=00:00:00.00 bitrate=N/A speed=N/frame=   77 fps=0.0 q=-0.0 size=     512kB time=00:00:05.13 bitrate= 817.1kbits/frame=  143 fps=142 q=-0.0 size=    1280kB time=00:00:09.53 bitrate=1099.9kbits/frame=  180 fps=143 q=-0.0 Lsize=    1905kB time=00:00:11.93 bitrate=1307.5kbits/s speed=9.47x    
video:1901kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.184620%

[Elon Musk]

Fixed in f56454544f35a3495310aa5ed4fb15e0ba7b967f