demux/mkv: use infinite chapter as last resort
demux/mkv: use infinite chapter as last resort

This fixes issues where you try to seek in an mkv that does not have a
duration (ie. where the last chapter just goes on and on), and it is
especially important for mkvs that only contains one chapter (that
goes on forever).

Prior to this patch these would not play at all.

Signed-off-by: Steve Lhomme <4317e33bca9d17016d37cb2d32c67dc65ca52d8e@videolabs.io>
Signed-off-by: Thomas Guillem <5f50a84c1fa3bcff146405017f36aec1a10a9e38@gllm.fr>

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc