avoid hypothetical problem with flushing queue with delayed events

src/switch_core_session.c

@@ -790,10 +790,17 @@ SWITCH_DECLARE(switch_status_t) switch_core_session_dequeue_message(switch_core_
 
 SWITCH_DECLARE(switch_status_t) switch_core_session_flush_message(switch_core_session_t *session)
 {
+	switch_status_t status = SWITCH_STATUS_FALSE;
+	void *pop;
 	switch_core_session_message_t *message;
 
-	while (switch_core_session_dequeue_message(session, &message) == SWITCH_STATUS_SUCCESS) {
-		switch_core_session_free_message(&message);
+	switch_assert(session != NULL);
+
+	if (session->message_queue) {
+		while ((status = (switch_status_t) switch_queue_trypop(session->message_queue, &pop)) == SWITCH_STATUS_SUCCESS) {
+			message = (switch_core_session_message_t *) pop;
+			switch_core_session_free_message(&message);
+		}
 	}
 
 	return SWITCH_STATUS_SUCCESS;