demux_mkv: use a single flag to indicate whether cues have been read

Before this commit, the demuxer would in theory accept multiple cues
elements (and append its contents to the index in the order as
encountered during reading). According to the Matroska specification,
there can be only one cues element in the segment, so this seems like
an overcomplication.

Change it so that redundant elements are ignored, like with all other
unique header elements. This makes implementing deferred reading of the
cues element easier.

0 files changed, 0 insertions, 0 deletions