Misaligned row artifacts showed up when a 624x352 frame was converted
to BGR24 format.  When advancing to the next row the destination linesize
was added to the last output pointer position which was not linesize aligned,
resulting in a distorted picture.
Signed-off-by: Pavel Koshevoy <pavel@apple.aragog.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>