wavarc: 8-bit 0CPY is not lossless

[ami_stuff]

​https://trac.ffmpeg.org/raw-attachment/ticket/10174/8_33_M_C0.WA

there is one difference between wa32.exe's output (decompressed input wav file) and ffmpeg's output

ffmpeg's output has additional 0 at the end:

./ffmpeg -i 8_33_M_C0.WA -f u8 -y out.raw
ffmpeg version N-109772-gc56f5be678 Copyright (c) 2000-2023 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.4.0-1ubuntu1~20.04.1)
  configuration: 
  libavutil      57. 44.100 / 57. 44.100
  libavcodec     59. 63.100 / 59. 63.100
  libavformat    59. 38.100 / 59. 38.100
  libavdevice    59.  8.101 / 59.  8.101
  libavfilter     8. 56.100 /  8. 56.100
  libswscale      6.  8.112 /  6.  8.112
  libswresample   4.  9.100 /  4.  9.100
Input #0, wavarc, from '8_33_M_C0.WA':
  Duration: N/A, start: 0.000000, bitrate: N/A
  Stream #0:0: Audio: wavarc (0CPY / 0x59504330), 33333 Hz, mono, u8p
Stream mapping:
  Stream #0:0 -> #0:0 (wavarc (native) -> pcm_u8 (native))
Press [q] to stop, [?] for help
Output #0, u8, to 'out.raw':
  Metadata:
    encoder         : Lavf59.38.100
  Stream #0:0: Audio: pcm_u8, 33333 Hz, mono, u8, 266 kb/s
    Metadata:
      encoder         : Lavc59.63.100 pcm_u8
size=     326kB time=00:00:09.98 bitrate= 267.1kbits/s speed= 694x    
video:0kB audio:326kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.000000%