In handleLeaveReq, remove session subscriptions directly.

Instead of writing to Session.detach.

server/topic.go

@@ -720,7 +720,7 @@ func (t *Topic) handleLeaveRequest(msg *ClientComMessage, sess *Session) {
 	// User wants to leave without unsubscribing.
 	if pssd, _ := t.remSession(sess, asUid); pssd != nil {
 		if !sess.isProxy() {
-			sess.detach <- t.name
+			sess.delSub(t.name)
 		}
 		if pssd.isChanSub != asChan {
 			// Cannot address non-channel subscription as channel and vice versa.

server/topic_proxy.go

@@ -139,7 +139,7 @@ func (t *Topic) handleProxyLeaveRequest(msg *ClientComMessage, killTimer *time.T
 	// and we won't be able to find and remove it by its sid.
 	pssd, result := t.remSession(msg.sess, asUid)
 	if result {
-		msg.sess.detach <- t.name
+		msg.sess.delSub(t.name)
 	}
 	if !msg.init {
 		// Explicitly specify the uid because the master multiplex session needs to know which