Fix FEC write return after merging RTX feedback changes

pkg/sfu/buffer/buffer.go

@@ -571,7 +571,7 @@ func (b *Buffer) writeFEC(fecPkt *rtp.Packet, arrivalTime int64) {
 
 	fecDelta, onFECRecovery := b.feedFECLocked(fecPkt, arrivalTime)
 	b.finishWriteLocked(arrivalTime, fecDelta, onFECRecovery)
-	return nil
+	return
 }
 
 // feedFECLocked runs a media or FEC packet through the FEC decoder and