Use saved_game::clear() to reset instead of creating a new object

Other such cases were also changed in 670bcf7.

src/game_initialization/multiplayer.cpp

@@ -623,7 +623,7 @@ void start_local_game_commandline(CVideo& video, const config& game_config, save
 	DBG_MP << "entering create mode" << std::endl;
 
 	// Set the default parameters
-	state = saved_game(); // This creates these parameters with default values defined in mp_game_settings.cpp
+	state.clear(); // This creates these parameters with default values defined in mp_game_settings.cpp
 	mp_game_settings& parameters = state.mp_settings();
 
 	// Hardcoded default values

src/gui/dialogs/multiplayer/mp_create_game.cpp

@@ -119,7 +119,7 @@ mp_create_game::mp_create_game(const config& cfg, ng::create_engine& create_eng)
 
 	create_engine_.init_active_mods();
 
-	create_engine_.get_state() = saved_game();
+	create_engine_.get_state().clear();
 	create_engine_.get_state().classification().campaign_type = game_classification::CAMPAIGN_TYPE::MULTIPLAYER;
 
 	// Need to set this in the constructor, pre_show() is too late

src/gui/dialogs/multiplayer/mp_join_game.cpp

@@ -133,7 +133,7 @@ bool mp_join_game::fetch_game_config(CVideo& video)
 	}
 
 	if(first_scenario_) {
-		state_ = saved_game();
+		state_.clear();
 		state_.classification() = game_classification(level_);
 
 		// Make sure that we have the same config as host, if possible.