Fix MessagesManager closing.

td/telegram/MessagesManager.cpp

@@ -12576,6 +12576,11 @@ void MessagesManager::tear_down() {
   parent_.reset();
 }
 
+void MessagesManager::hangup() {
+  postponed_channel_updates_.clear();
+  stop();
+}
+
 void MessagesManager::start_up() {
   init();
 }

td/telegram/MessagesManager.h

@@ -2789,9 +2789,13 @@ class MessagesManager final : public Actor {
   void on_message_ttl_expired_impl(Dialog *d, Message *m);
 
   void start_up() final;
+
   void loop() final;
+
   void tear_down() final;
 
+  void hangup() final;
+
   void create_folders();
   void init();