MKV: send the proper PCR before es_out_Send() of the packet

MKV: send the proper PCR before es_out_Send() of the packet

replaces previous similar patches, now with proper VLC_TS adjusting

Fixes #13575
Fixes #11847 which had time display issues

The new PCR logic is borrowed from
http://git.videolan.org/?p=vlc.git;a=blob;f=modules/demux/avformat/demux.c;hb=HEAD#l776

A PCR is always sent now, unless i_last_dts is not set, meaning the first
packet doesn't have a proper DTS (invalid data at the beggining)

The i_pts is not set to 0 anymore in a lace as it disturbs seeking performance

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>