EnableGameSound in PIE settings won't work after LoadMap is called

When PIE is started with the Enable Game Sound box unchecked, we set master volume to 0 to mute game sounds. However, any call to LoadMap will both flush the audio device and set the volume back to 1. As a result, any action that leads to a LoadMap call will unmute the audio. This could be directly opening a new map, or starting PIE with multiple clients where those clients will need to load the map themselves.

1. In Editor Preferences under Play in Editor, uncheck Enable Game Sound
2. Check the box for Use Single Process (Or use the open console command to load a different map)
3. Note that audio now continues to play during PIE