assrender: no subs after seek back to 0
To reproduce: gst-play-1.0 assrender-test.mkv, play for 10-20 seconds, note subs, then hit 0 to seek back to the start and see how there are no subs.
To reproduce: gst-play-1.0 assrender-test.mkv, play for 10-20 seconds, note subs, then hit 0 to seek back to the start and see how there are no subs.