avformat/utils: do not wait for packets from discarded streams for genpts

Fixes long loop
Fixes Ticket3208

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 8202c49b43621c04e26d4a3aa83a10e1e5cc1836)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
1 file changed