receive_policy must provide an invalid_msg_do_what method

chat_networking.hpp

@@ -171,6 +171,8 @@ namespace chat
                                  receive_policy::logout_do_what
                                          (chat_message(message::LOGOUT, content));
                                  break;
+                             default:
+                                 receive_policy::invalid_msg_do_what(msg);
                          }
 
                          for (auto& fun : _subscriptions)               // notify subscribers