splitmuxsink: Split fragment only if queued time is larger than threshold

splitmuxsink: Split fragment only if queued time is larger than threshold

The queued time includes the duration of the last queued frame
(i.e., new keyframe) so the condition check should not be inclusive.
Note that the new fragment will be cut excluding the last frame
and therefore if the condition is inclusive way,
the fragment might have one frame shorter duration for all keyframe
stream such as jpeg or all-inter video streams.