wesnothd: avoid trying to remove destructed players from games during stack unwinding

src/server/wesnothd/game.hpp

@@ -588,6 +588,12 @@ public:
 	 */
 	bool is_reload() const;
 
+	void emergency_cleanup()
+	{
+		players_.clear();
+		observers_.clear();
+	}
+
 private:
 	// forbidden operations
 	game(const game&) = delete;

src/server/wesnothd/server.cpp

@@ -1387,6 +1387,8 @@ void server::cleanup_game(game* game_ptr)
 		LOG_SERVER << "Could not find game (" << game_ptr->id() << ", " << game_ptr->db_id() << ") to delete in games_and_users_list_.\n";
 	}
 
+	if(destructed) game_ptr->emergency_cleanup();
+
 	delete game_ptr;
 }