When there are gaps between segments in the DASH manifest (e.g. it's a recording of a live stream during which the camera was turned on and off a couple times), seeking to a timestamp that belongs into a gap leads to repeat_index calculation yielding a nonsensical negative number (because ts < segment->start). In such event set the playback to continue at the first repetition of the segment that follows after the gap. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8620>