use config::child_or_add

Note: This commit is a squash of two cherry-picked commits
from master, they were adjacent and the second was a fixup
of the first. The first commit in master was
28ffcc5

src/playcampaign.cpp

@@ -271,15 +271,10 @@ static LEVEL_RESULT playsingle_scenario(const config& game_config,
 	LOG_NG << "created objects... " << (SDL_GetTicks() - playcontroller.get_ticks()) << "\n";
 
 	LEVEL_RESULT res = playcontroller.play_scenario(story, skip_replay);
-	end_level = playcontroller.get_end_level_data_const();
 
-	if (state_of_game.carryover_sides.has_child("end_level_data")) {
-		config& cfg_end_level = state_of_game.carryover_sides.child("end_level_data");
-		end_level.write(cfg_end_level);
-	} else {
-		config& cfg_end_level = state_of_game.carryover_sides.add_child("end_level_data");
-		end_level.write(cfg_end_level);
-	}
+	end_level = playcontroller.get_end_level_data_const();
+	config& cfg_end_level = state_of_game.carryover_sides.child_or_add("end_level_data");
+	end_level.write(cfg_end_level);
 
 	if (res == DEFEAT) {
 		if (resources::persist != NULL)
@@ -324,15 +319,10 @@ static LEVEL_RESULT playmp_scenario(const config& game_config,
 	playmp_controller playcontroller(init_level, state_of_game, ticks, num_turns,
 		game_config, disp.video(), skip_replay, blindfold_replay, io_type == IO_SERVER);
 	LEVEL_RESULT res = playcontroller.play_scenario(story, skip_replay);
-	end_level = playcontroller.get_end_level_data_const();
 
-	if (state_of_game.carryover_sides.has_child("end_level_data")) {
-		config& cfg_end_level = state_of_game.carryover_sides.child("end_level_data");
-		end_level.write(cfg_end_level);
-	} else {
-		config& cfg_end_level = state_of_game.carryover_sides.add_child("end_level_data");
-		end_level.write(cfg_end_level);
-	}
+	end_level = playcontroller.get_end_level_data_const();
+	config& cfg_end_level = state_of_game.carryover_sides.child_or_add("end_level_data");
+	end_level.write(cfg_end_level);
 
 	//Check if the player started as mp client and changed to host
 	if (io_type == IO_CLIENT && playcontroller.is_host())