Try to read header elements stored at the end of the file in the order
of their position. (It would be nicer if mkv simply told us a range of
elements to parse, but it doesn't do that.)
This can potentially reduce seek elements, although I didn't check if
any real files trigger this. The real contribution by this change is
that it does not defer reading the CUE index if we need to seek to the
end of the file anyway. This can actually avoid 2 seeks when opening a
file and --start is used, and the file has other headers elements at the
end of the file (like tags).
6fe75c38d8