Wrong timestamps for G.729 in wav

[Carl Eugen Hoyos]

When decoding the sample from ticket #4577, many warnings are shown, the final output duration is wrong, should be 2:15.

$ ffmpeg -i 222.vd8 out.wav
ffmpeg version N-74268-gf6518e5 Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl
  libavutil      54. 30.100 / 54. 30.100
  libavcodec     56. 57.100 / 56. 57.100
  libavformat    56. 40.101 / 56. 40.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 32.100 /  5. 32.100
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.101 /  1.  2.101
  libpostproc    53.  3.100 / 53.  3.100
[wav @ 0x24a41c0] ignoring wrong sample_count 135200
[wav @ 0x24a41c0] Estimating duration from bitrate, this may be inaccurate
Guessed Channel Layout for  Input Stream #0.0 : mono
Input #0, wav, from '222.vd8':
  Duration: 00:02:15.20, bitrate: 8 kb/s
    Stream #0:0: Audio: g729 ([154]r[0][0] / 0x729A), 8000 Hz, 1 channels, s16, 8 kb/s
Output #0, wav, to 'out.wav':
  Metadata:
    ISFT            : Lavf56.40.101
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 8000 Hz, mono, s16, 128 kb/s
    Metadata:
      encoder         : Lavc56.57.100 pcm_s16le
Stream mapping:
  Stream #0:0 -> #0:0 (g729 (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
[output stream 0:0 @ 0x248f740] 100 buffers queued in output stream 0:0, something may be wrong.
[wav @ 0x24d2720] Non-monotonous DTS in output stream 0:0; previous: 32560, current: 80; changing to 32560. This may result in incorrect timestamps in the output file.
[wav @ 0x24d2720] Non-monotonous DTS in output stream 0:0; previous: 32560, current: 160; changing to 32560. This may result in incorrect timestamps in the output file.

...

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[wav @ 0x24d2720] Non-monotonous DTS in output stream 0:0; previous: 35120, current: 6960; changing to 35120. This may result in incorrect timestamps in the output file.
[wav @ 0x24d2720] Non-monotonous DTS in output stream 0:0; previous: 35120, current: 7040; changing to 35120. This may result in incorrect timestamps in the output file.
size=    2113kB time=00:00:04.40 bitrate=3933.2kbits/s
video:0kB audio:2112kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.003606%

[Ganesh Ajjanagadde]

Fixed in 0581ab2cacccb96740ef246972f12d7a34f1cc0f.

Thanks!