Always instantiate nacker when using out-of-band sequence numbers. (#4187)

pkg/sfu/buffer/buffer_base.go

@@ -386,6 +386,10 @@ func (b *BufferBase) BindLocked(rtpParameters webrtc.RTPParameters, codec webrtc
 		}
 	}
 
+	if b.nacker == nil && b.params.IsOOBSequenceNumber {
+		b.nacker = nack.NewNACKQueue(nack.NackQueueParamsDefault)
+	}
+
 	b.StartKeyFrameSeeder()
 
 	return nil