Don't drop dummy packets (#760)

Rely on increasing timestamps instead

Author: milos-lk

pkg/synchronizer/track.go

@@ -137,11 +137,6 @@ func (t *TrackSynchronizer) OnSenderReport(f func(drift time.Duration)) {
 // dropped while waiting, and a boolean indicating whether the track is ready to
 // process samples. After the gate finishes, there is no need to call the API again.
 func (t *TrackSynchronizer) PrimeForStart(pkt jitter.ExtPacket) ([]jitter.ExtPacket, int, bool) {
-	if !t.initialized && len(pkt.Payload) == 0 {
-		// skip dummy packets until the track is initialized
-		return nil, 0, false
-	}
-
 	if t.initialized || t.startGate == nil {
 		if !t.initialized {
 			t.Initialize(pkt.Packet)