demux/mkv: fix assert on infinite clusters
demux/mkv: fix assert on infinite clusters

A cluster can have an infinite size, and if so the result of invoking
KaxCluster::GetEndPosition is undefined. These changes simply make
sure that we do not query clusters for their size, if they are not
finite in size.

fixes #17537

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