qtdemux: Don't skip track regardless of duration

All the boxes in the 'trak' container should be parsed regardless of
whether its duration is shorter than the duration of the longest track.
8 jobs from support-short-stream in 14 minutes and 2 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Preparation
passed #124509
gst indent

00:00:27

passed #124508
manifest

00:00:17

 
  Build
passed #124510
build fedora x86_64

00:03:12

 
  Test
passed #124511
check fedora

00:03:24

 
  Full Builds
passed #124512
build android arm64 api28

00:03:26

passed #124514
build cerbero cross win32

00:05:11

passed #124515
build cerbero cross win64

00:06:03

passed #124513
build cerbero fedora x86_64

00:06:57