demux: ogg: fix PCR from opus granule.
demux: ogg: fix PCR from opus granule.

Can't use granule 0 as it means there's still no valid first sample
after processing packet.
Fix start gap on opus webradios.

shyamalschandra/vlc,vlc-mirror/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,krichter722/vlc,vlc-mirror/vlc,shyamalschandra/vlc,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,shyamalschandra/vlc,krichter722/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,krichter722/vlc,krichter722/vlc,xkfz007/vlc,vlc-mirror/vlc,krichter722/vlc,vlc-mirror/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,jomanmuk/vlc-2.2,krichter722/vlc,shyamalschandra/vlc,xkfz007/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc