stream, so as to calculate the duration, don't stop
as soon as all streams have seen at least on packet.
Otherwise the duration will be shorter than it
should be.  We must keep reading to the end-of-file.
patch by neilb suse de


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@10139 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b