multiqueue: Ignore duplicate SEGMENT event
Some elements (such as qtdemux) re-send identical SEGMENT events which would cause our internal position tracking to be resetted.
This would cause the input/output position to be sporadically resetted, and therefore the time level to (wrongly) change. This could lead to temporary (wrong) buffering messages to be posted.
In order to avoid this, check whether the segment to apply is really different (except for the position/duration).