fix key frame timer (#2662)

pkg/sfu/downtrack.go

@@ -627,12 +627,11 @@ func (d *DownTrack) keyFrameRequester() {
 	}
 
 	timer := time.NewTimer(math.MaxInt64)
+	timer.Stop()
+
 	defer timer.Stop()
 
 	for !d.IsClosed() {
-		if !timer.Stop() {
-			<-timer.C
-		}
 		timer.Reset(getInterval())
 
 		select {
@@ -640,6 +639,9 @@ func (d *DownTrack) keyFrameRequester() {
 			if !more {
 				return
 			}
+			if !timer.Stop() {
+				<-timer.C
+			}
 		case <-timer.C:
 		}