ogg: Fix potential infinite discard loop

ogg: Fix potential infinite discard loop

Seeking in certain broken files would cause ogg_read_timestamp
to fail because ogg_packet would go into a state where all packets
of stream 1 would be discarded until the end of the stream.

Bug-Id: 553
CC: libav-stable@libav.org
Signed-off-by: Jan Gerber <j@v2v.cc>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
(cherry picked from commit 9a27acae9e6b7d0bf74c5b878af9c42495a546f3)
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
Conflicts:
	libavformat/oggdec.c