mkvparser: fix int64 -> unsigned conversion warnings

in 32-bit builds:
mkvparser\mkvparser.cc(1536,42): warning C4244: 'initializing':
conversion from '__int64' to 'unsigned int', possible loss of data

the counts have previously been range checked since:
566a1e0 Add checks for overflow during parsing

Change-Id: Ib185df3f95869fba3a26ab09a1a555e5b550ebf1
1 file changed