Incorrect colours when padding for yuvj4xx

[Carl Eugen Hoyos]

​http://ffmpeg.org/pipermail/ffmpeg-user/2016-June/032416.html
The pad filter accepts yuvj4xx as input format but uses yuv4xx data and produces gray output.

$ ffmpeg -f lavfi -i color=s=4x4:color=white -vf format=yuvj420p,scale,pad=1920:1080:color=white -f rawvideo -vframes 1 out
ffmpeg version N-80268-g9e9286e Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl
  libavutil      55. 24.100 / 55. 24.100
  libavcodec     57. 46.100 / 57. 46.100
  libavformat    57. 37.101 / 57. 37.101
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 46.101 /  6. 46.101
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, lavfi, from 'color=s=4x4:color=white':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 4x4 [SAR 1:1 DAR 1:1], 25 tbr, 25 tbn, 25 tbc
[swscaler @ 0x37126c0] deprecated pixel format used, make sure you did set range correctly
[rawvideo @ 0x3704e40] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
Output #0, rawvideo, to 'out':
  Metadata:
    encoder         : Lavf57.37.101
    Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuvj420p, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 25 fps, 25 tbn, 25 tbc
    Metadata:
      encoder         : Lavc57.46.100 rawvideo
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> rawvideo (native))
Press [q] to stop, [?] for help
[swscaler @ 0x37126c0] Warning: data is not aligned! This can lead to a speedloss
frame=    1 fps=0.0 q=-0.0 Lsize=    3038kB time=00:00:00.04 bitrate=622080.0kbits/s speed=12.2x
video:3038kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.000000%

$ hexdump -C out
00000000  ff ff ff ff eb eb eb eb  eb eb eb eb eb eb eb eb  |................|
00000010  eb eb eb eb eb eb eb eb  eb eb eb eb eb eb eb eb  |................|
*
00000780  ff ff ff ff eb eb eb eb  eb eb eb eb eb eb eb eb  |................|
00000790  eb eb eb eb eb eb eb eb  eb eb eb eb eb eb eb eb  |................|
*
00000f00  ff ff ff ff eb eb eb eb  eb eb eb eb eb eb eb eb  |................|
00000f10  eb eb eb eb eb eb eb eb  eb eb eb eb eb eb eb eb  |................|
*
00001680  ff ff ff ff eb eb eb eb  eb eb eb eb eb eb eb eb  |................|
00001690  eb eb eb eb eb eb eb eb  eb eb eb eb eb eb eb eb  |................|
*
001fa400  80 80 80 80 80 80 80 80  80 80 80 80 80 80 80 80  |................|
*
002f7600

[Elon Musk]

Fixed in f43fd68f28079c49e9237894a294968d841babc7.