bmp rle: fix decoding of 4bpp with flipped row order

[ami_stuff]

C:\>ffmpeg -i 4bpp_rle_flip_order.bmp -y out.bmp
ffmpeg version N-54766-g4f1d3e0 Copyright (c) 2000-2013 the FFmpeg developers
  built on Jul 16 2013 02:39:32 with gcc 4.5.0 (GCC) 20100414 (Fedora MinGW 4.5.
0-1.fc14)
  configuration: --prefix=/var/www/users/research/ffmpeg/snapshots/build --arch=
x86 --target-os=mingw32 --cross-prefix=i686-pc-mingw32- --cc='ccache i686-pc-min
gw32-gcc' --enable-w32threads --enable-memalign-hack --enable-runtime-cpudetect
--enable-cross-compile --enable-static --disable-shared --extra-libs='-lws2_32 -
lwinmm -lpthread' --extra-cflags='--static -I/var/www/users/research/ffmpeg/snap
shots/build/include' --extra-ldflags='-static -L/var/www/users/research/ffmpeg/s
napshots/build/lib' --enable-bzlib --enable-zlib --enable-gpl --enable-version3
--enable-nonfree --enable-libx264 --enable-libspeex --enable-libtheora --enable-
libvorbis --enable-libfaac --enable-libxvid --enable-libopencore-amrnb --enable-
libopencore-amrwb --enable-libmp3lame --enable-libvpx --disable-decoder=libvpx
  libavutil      52. 39.100 / 52. 39.100
  libavcodec     55. 18.102 / 55. 18.102
  libavformat    55. 12.102 / 55. 12.102
  libavdevice    55.  3.100 / 55.  3.100
  libavfilter     3. 81.101 /  3. 81.101
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
[bmp @ 0x20ec320] MS RLE: ended frame decode with 35878 bytes left over
Input #0, image2, from '4bpp_rle_flip_order.bmp':
  Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: bmp, pal8, 320x240, 25 tbr, 25 tbn, 25 tbc
Output #0, image2, to 'out.bmp':
  Metadata:
    encoder         : Lavf55.12.102
    Stream #0:0: Video: bmp, pal8, 320x240, q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (bmp -> bmp)
Press [q] to stop, [?] for help
[bmp @ 0x20ec320] MS RLE: ended frame decode with 35878 bytes left over
frame=    1 fps=0.0 q=-1.0 Lsize=N/A time=00:00:00.04 bitrate=N/A
video:76kB audio:0kB subtitle:0 global headers:0kB muxing overhead -100.028249%

[Carl Eugen Hoyos]

FFmpeg 0.5 showed a flipped image.

[Carl Eugen Hoyos]

Fixed by you in 5f39992.