Better way to leave the dummy room

src/bridge/bridge.cpp

@@ -44,7 +44,9 @@ void Bridge::shutdown()
 {
   for (auto it = this->irc_clients.begin(); it != this->irc_clients.end(); ++it)
   {
-    it->second->send_quit_command("Gateway shutdown");
+    const std::string exit_message("Gateway shutdown");
+    it->second->send_quit_command(exit_message);
+    it->second->leave_dummy_channel(exit_message);
   }
 }