aic: fix artefacts when height is not multiply of 16

[ami_stuff]

​https://trac.ffmpeg.org/raw-attachment/ticket/6093/aic_320.7z
​https://trac.ffmpeg.org/raw-attachment/ticket/6093/aic_320_2.7z

C:\>ffmpeg -i  C:\aic_320_247.mov out.bmp
ffmpeg version 3.2.git Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 4.6.2 (GCC)
  configuration: --disable-pthreads --enable-gpl --disable-ffprobe
  libavutil      55. 47.100 / 55. 47.100
  libavcodec     57. 81.100 / 57. 81.100
  libavformat    57. 66.102 / 57. 66.102
  libavdevice    57.  2.100 / 57.  2.100
  libavfilter     6. 73.100 /  6. 73.100
  libswscale      4.  3.101 /  4.  3.101
  libswresample   2.  4.100 /  2.  4.100
  libpostproc    54.  2.100 / 54.  2.100
[aic @ 0237d680] Warning: not compiled with thread support, using thread emulati
on
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'C:\aic_320_247.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 537199360
    compatible_brands: qt
    creation_time   : 2017-02-20T11:52:11.000000Z
  Duration: 00:00:00.07, start: 0.000000, bitrate: 1620 kb/s
    Stream #0:0(eng): Video: aic (icod / 0x646F6369), yuv420p(progressive), 320x
247, 1520 kb/s, 15 fps, 15 tbr, 600 tbn, 600 tbc (default)
    Metadata:
      creation_time   : 2017-02-20T11:52:11.000000Z
      handler_name    : Apple Alias Data Handler
      encoder         : Apple Intermediate Codec
File 'out.bmp' already exists. Overwrite ? [y/N] y
[aic @ 0237b940] Warning: not compiled with thread support, using thread emulati
on
[bmp @ 027094c0] Warning: not compiled with thread support, using thread emulati
on
Output #0, image2, to 'out.bmp':
  Metadata:
    major_brand     : qt
    minor_version   : 537199360
    compatible_brands: qt
    encoder         : Lavf57.66.102
    Stream #0:0(eng): Video: bmp, bgr24, 320x247, q=2-31, 200 kb/s, 15 fps, 15 t
bn, 15 tbc (default)
    Metadata:
      creation_time   : 2017-02-20T11:52:11.000000Z
      handler_name    : Apple Alias Data Handler
      encoder         : Lavc57.81.100 bmp
Stream mapping:
  Stream #0:0 -> #0:0 (aic (native) -> bmp (native))
Press [q] to stop, [?] for help
frame=    1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.06 bitrate=N/A speed=N/A
video:232kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing o
verhead: unknown