Since decoding is doing from the end and aligned by 16
previous code worked correctly only when picture height was dividable by 16,
otherwise it provides garbage in top lines and truncates bottom.
New code adjusts data[] pointers taking in account alignment issue.



git-svn-id: file:///var/local/repositories/ffmpeg/trunk@10727 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b