rv20: 1-framed rv20 svt does not decode

[ami_stuff]

rv20 (not svt) decodes correctly

C:\>ffmpeg -i C:\g2svt_1frame.rm out.avi
ffmpeg version 3.2.git Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 4.6.2 (GCC)
  configuration: --disable-pthreads --disable-ffprobe --enable-gpl
  libavutil      55. 48.100 / 55. 48.100
  libavcodec     57. 83.100 / 57. 83.100
  libavformat    57. 66.104 / 57. 66.104
  libavdevice    57.  3.100 / 57.  3.100
  libavfilter     6. 76.100 /  6. 76.100
  libswscale      4.  3.101 /  4.  3.101
  libswresample   2.  4.100 /  2.  4.100
  libpostproc    54.  2.100 / 54.  2.100
[rm @ 02383d20] Invalid stream index 2 for index at pos 4250
[sipr @ 0238d300] Warning: not compiled with thread support, using thread emulat
ion
[rv20 @ 027188c0] Warning: not compiled with thread support, using thread emulat
ion
Input #0, rm, from 'C:\g2svt_1frame.rm':
  Metadata:
    Target Audiences: 28K Modem (20 Kbps);
    Audio Format    : Voice Only
    Video Quality   : Smoothest Motion Video
    Creation Date   : 3/16/2017 14:41:21
    Modification Date: 3/16/2017 14:41:21
    Generated By    : RealMedia Build Engine 6.0.11.201 Windows
    File ID         : bc5f1b6d-05a0-f0df-1fd5-1f68b3c48742
    title           :
    author          :
    copyright       :
    comment         :
  Duration: 00:00:02.88, start: 0.000000, bitrate: 11 kb/s
    Stream #0:0: Audio: sipr (sipr / 0x72706973), 8000 Hz, mono, flt, 4 kb/s
    Stream #0:1: Video: rv20 (RV20 / 0x30325652), yuv420p, 176x144, 15 kb/s, 15
fps, 15 tbr, 1k tbn, 1k tbc
[sipr @ 02719fc0] Warning: not compiled with thread support, using thread emulat
ion
[rv20 @ 02386580] Warning: not compiled with thread support, using thread emulat
ion
Stream mapping:
  Stream #0:1 -> #0:0 (rv20 (native) -> mpeg4 (native))
  Stream #0:0 -> #0:1 (sipr (native) -> ac3 (native))
Press [q] to stop, [?] for help
[ac3 @ 0238e440] Warning: not compiled with thread support, using thread emulati
on
Finishing stream 0:0 without any data written to it.
[mpeg4 @ 027269e0] Warning: not compiled with thread support, using thread emula
tion
Output #0, avi, to 'out.avi':
  Metadata:
    Target Audiences: 28K Modem (20 Kbps);
    Audio Format    : Voice Only
    Video Quality   : Smoothest Motion Video
    Creation Date   : 3/16/2017 14:41:21
    Modification Date: 3/16/2017 14:41:21
    Generated By    : RealMedia Build Engine 6.0.11.201 Windows
    File ID         : bc5f1b6d-05a0-f0df-1fd5-1f68b3c48742
    INAM            :
    author          :
    ICOP            :
    ICMT            :
    ISFT            : Lavf57.66.104
    Stream #0:0: Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 176x144, q=2-31, 200
 kb/s, 15 fps, 15 tbn, 15 tbc
    Metadata:
      encoder         : Lavc57.83.100 mpeg4
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
    Stream #0:1: Audio: ac3 ([0] [0][0] / 0x2000), 8000 Hz, mono, fltp, 96 kb/s
    Metadata:
      encoder         : Lavc57.83.100 ac3
frame=    0 fps=0.0 q=0.0 Lsize=      44kB time=00:00:02.88 bitrate= 124.5kbits/
s speed=8.38x
video:0kB audio:34kB subtitle:0kB other streams:0kB global headers:0kB muxing ov
erhead: 29.733797%