[MCL-5477] Launcher prints complete log after shutdown when custom log config does not output XML

Affected version: 2.0.757-stage (Windows)

The bug

The launcher prints the complete log as a single log line after closing the game when the custom log config outputs a formatted log line with a PatternLayout and "Custom log config outputs XML" (launch.label.custom_log_config_is_xml) is enabled.

16:58:07	launcher	Preparing to launch minecraft client for 1.11.2
16:58:07	launcher	Minecraft client 1.11.2 is ready to start.
16:58:08	launcher	Using custom game log configuration ###\client-test.xml (outputs XML)
16:58:18	launcher	Process closed with exit code 0
16:58:18	launcher	[16:58:09] [Client thread/INFO]: Setting user: Marcono1234
				[16:58:10] [Client thread/INFO]: LWJGL Version: 2.9.4
				[16:58:10] [Client thread/INFO]: Reloading ResourceManager: Default
				[16:58:11] [Sound Library Loader/INFO]: Starting up SoundSystem...
				[16:58:11] [Thread-5/INFO]: Initializing LWJGL OpenAL
				[16:58:11] [Thread-5/INFO]: (The LWJGL binding of OpenAL.  For more information, see http://www.lwjgl.org)
				[16:58:11] [Thread-5/INFO]: OpenAL initialized.
				[16:58:11] [Sound Library Loader/INFO]: Sound engine started
				[16:58:14] [Client thread/INFO]: Created: 1024x512 textures-atlas
				[16:58:17] [Client thread/INFO]: Stopping!
				[16:58:17] [Client thread/INFO]: SoundSystem shutting down...
				[16:58:17] [Client thread/WARN]: Author: Paul Lamb, www.paulscode.com

How to reproduce

Enable advanced settings
Use the attached client-test.xml file as log config for a profile
Enable "Custom log config outputs XML"
Start the profile
Close Minecraft
→ The complete game log should appear as a single log line