ljpeg: fix 12/16bpp decoding for images with odd width

[ami_stuff]

there is a vertical line on the right side in the output tiff image

https://ffmpeg.org/trac/ffmpeg/attachment/ticket/855/12_line.jpg
https://ffmpeg.org/trac/ffmpeg/attachment/ticket/855/16_line.jpg

ffmpeg -i 12_line.jpg out.tif
ffmpeg version 0.9.0.git-dc7ad85, Copyright (c) 2000-2012 the FFmpeg developers
  built on Jan  4 2012 22:15:52 with gcc 4.5.0
  libavutil      51. 34.100 / 51. 34.100
  libavcodec     53. 50.100 / 53. 50.100
  libavformat    53. 29.100 / 53. 29.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 57.101 /  2. 57.101
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  5.100 /  0.  5.100
  libpostproc    51.  2.100 / 51.  2.100
[mjpeg @ 0x10fef3e0] Warning: not compiled with thread support, using thread emulation
Input #0, image2, from '12_line.jpg':
  Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
Codec 0x8 is not in the full list.
    Stream #0:0: Video: mjpeg, gray16be, 639x439, 25 tbr, 25 tbn, 25 tbc
Incompatible pixel format 'gray16be' for codec 'tiff', auto-selecting format 'rgb48le'
[buffer @ 0x10ff1c60] w:639 h:439 pixfmt:gray16be tb:1/1000000 sar:0/1 sws_param:
[buffersink @ 0x10ff1fe0] auto-inserting filter 'auto-inserted scale 0' between the filter 'src' and the filter 'out'
[scale @ 0x10ff2560] w:639 h:439 fmt:gray16be -> w:639 h:439 fmt:rgb48le flags:0x4
[tiff @ 0x10ff0be0] Warning: not compiled with thread support, using thread emulation
[mjpeg @ 0x10fef3e0] Warning: not compiled with thread support, using thread emulation
Output #0, image2, to 'out.tif':
  Metadata:
    encoder         : Lavf53.29.100
Codec 0x62 is not in the full list.
    Stream #0:0: Video: tiff, rgb48le, 639x439, q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (mjpeg -> tiff)
Press [q] to stop, [?] for help
frame=    1 fps=  0 q=0.0 Lsize=       0kB time=00:00:00.04 bitrate=   0.0kbits/s    
video:1578kB audio:0kB global headers:0kB muxing overhead -100.000000%

[ami_stuff]

this is actually a bug in swscale (anything to rgb48le) triggered when input have odd width

ffmpeg -i 599.png -pif_fmt rgb48le out.tif

[ami_stuff]

Fixed in 9206ac80a5c3256738b887cf3cfe39f385ebc672.

swscale: handle last pixel if lines have an odd width.