If a sequence of JXL images is encapsulated in a container that has PTS
information, we should use the PTS information from the container. At
this time there is no container that does this, but if JPEG XL support
is ever added to NUT, AVTransport, or some other container, this commit
should allow the PTS information those containers provide to work as
expected.
Signed-off-by: Leo Izen <leo.izen@gmail.com>