fix aac playback regression

Discussed at http://comments.gmane.org/gmane.comp.video.ffmpeg.devel/103768

related reports:
 - http://bugs.debian.org/540729
 - https://roundup.ffmpeg.org/roundup/ffmpeg/issue800



Originally committed as revision 21706 to svn://svn.ffmpeg.org/ffmpeg/branches/0.5
2 files changed