Update only the queue ID in settings.cfg

Saving a new queue ID wrote every setting from memory, which could also save
a setting that is in use but not saved yet, like the debug winning score.
Now it loads the file, changes only the queue ID and saves it again.

data/settings.gd

@@ -181,10 +181,19 @@ func save_settings() -> void:
 		GameLog.warning("Could not save the settings to %s: %s" % [path, error_string(error)])
 
 
-## Sets the play queue ID for [param server] and saves it.
+## Sets the play queue ID for [param server] and saves it. Only the ID is changed in
+## the file; the other settings in it stay as they were saved.
 func set_queue_id(server: String, id: String) -> void:
 	queue_ids[server] = id
-	save_settings()
+	var path: String = saved_settings_path()
+	var file: ConfigFile = ConfigFile.new()
+	# A missing file is fine: it is written with only the queue ID
+	file.load(path)
+	file.set_value("queues", server, id)
+	DirAccess.make_dir_recursive_absolute(path.get_base_dir())
+	var error: Error = file.save(path)
+	if error != OK:
+		GameLog.warning("Could not save the queue ID to %s: %s" % [path, error_string(error)])
 
 
 ## Turns fullscreen on or off and saves it.