[REALMS-12239] Crash on clicking on Realms button

Step to reproduce

Enter Game with Official 1.13
Go into Minecraft Realms

And the game instantly crashed

Description: Rendering screen

java.lang.IllegalStateException: Child not present in child list:com.mojang.realmsclient.RealmsMainScreen$ServerSelectionList@2cf09576
	at cio.b(SourceFile:180)
	at net.minecraft.realms.RealmsScreen.removeWidget(SourceFile:176)
	at com.mojang.realmsclient.RealmsMainScreen.drawPopup(RealmsMainScreen.java:978)
	at com.mojang.realmsclient.RealmsMainScreen.render(RealmsMainScreen.java:846)
	at cio.a(SourceFile:99)
	at ctn.a(SourceFile:792)
	at cfi.c(SourceFile:847)
	at cfi.a(SourceFile:392)
	at net.minecraft.client.main.Main.main(SourceFile:144)