I added a config option vai menu lib for resource location to class name. So it should be working

Issue:
Main menu plays sounds your music right after switching from your menu to vanilla's
I called Minecraft.getMinecraft().getSoundHandler().stopSounds(); before switching menus

Steps on how to reproduce:
install evil notch lib beta latest SNAPSHOT 44
add this code to menu lib folder > menulib.cfg config "thebetweenlands:mainmenu" = "thebetweenlands.client.gui.menu.GuiBLMainMenu"
Launch
Notice mc main menu shows up plays mc music
Switch to your main menu your music plays
Go back to mc wait a while then your music plays again instead of vanilla on the vanilla menu and there is no fixing it without a restart

Solution:
always check each tick if your in the main menu not set it true once always assume it's going to be true. Just always check it because main menus can switch
#627

Why: menu lib allows switching main menus in game so you need to constantly check mc's current gui before playing sounds

this pull fixes this:
#627