add a function to tell if there's app data in the retransmission queue

retransmission_queue.go

@@ -47,6 +47,10 @@ func (q *retransmissionQueue) HasHandshakeData() bool {
 	return len(q.handshakeCryptoData) > 0 || len(q.handshake) > 0
 }
 
+func (q *retransmissionQueue) HasAppData() bool {
+	return len(q.appData) > 0
+}
+
 func (q *retransmissionQueue) AddAppData(f wire.Frame) {
 	if _, ok := f.(*wire.StreamFrame); ok {
 		panic("STREAM frames are handled with their respective streams.")