vmix: broken output with 7680x4320 resolution

[ami_stuff]

decodes ok with the original codec

./ffmpeg -i 7680_4320.avi -y out.avi
ffmpeg version N-112010-g1a87a9d82a Copyright (c) 2000-2023 the FFmpeg developers
  built with gcc 11 (Ubuntu 11.4.0-1ubuntu1~22.04)
  configuration: 
  libavutil      58. 19.100 / 58. 19.100
  libavcodec     60. 26.100 / 60. 26.100
  libavformat    60. 11.100 / 60. 11.100
  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
Input #0, avi, from '7680_4320.avi':
  Metadata:
    software        : Lavf58.76.100
  Duration: 00:00:00.04, start: 0.000000, bitrate: 434257 kb/s
  Stream #0:0: Video: vmix (VMX1 / 0x31584D56), yuv422p, 7680x4320, 25 fps, 25 tbr, 25 tbn
Stream mapping:
  Stream #0:0 -> #0:0 (vmix (native) -> mpeg4 (native))
Press [q] to stop, [?] for help
Output #0, avi, to 'out.avi':
  Metadata:
    software        : Lavf58.76.100
    ISFT            : Lavf60.11.100
  Stream #0:0: Video: mpeg4 (FMP4 / 0x34504D46), yuv420p(tv, progressive), 7680x4320, q=2-31, 200 kb/s, 25 fps, 25 tbn
    Metadata:
      encoder         : Lavc60.26.100 mpeg4
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: N/A
frame=    0 fps=0.0 q=14.3 size=       0kB time=00:00:00.00 bitrate=N/A speed=  [out#0/avi @ 0x55ea37803240] video:348kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.600830%
frame=    1 fps=0.0 q=14.3 Lsize=     354kB time=00:00:00.00 bitrate=N/A speed=   0x    

[Elon Musk]

Fixed in 86bd0f08d3ea3dfdd523a1b1ac9e52545641c443