[MC-187406] Game crashes when joining in disabled dimension

1. Add testpack2 datapack to world on creation
2. Join custom dimension with `/execute in custom:lol run tp @s ~ ~ ~`
3. Disable pack with `/datapack disable <tab>` and leave the world
4. Rejoin the world and game crashes

Datapack was sourced from https://github.com/RainWarrior/test/tree/sure

Time: 6/4/20 11:28 PM
Description: Ticking memory connection

java.lang.NullPointerException: Ticking memory connection
	at abp.a(SourceFile:150)
	at zx.c(SourceFile:111)
	at zx.b(SourceFile:63)
	at me.a(SourceFile:230)
	at zu.c(SourceFile:171)
	at net.minecraft.server.MinecraftServer.b(SourceFile:885)
	at net.minecraft.server.MinecraftServer.a(SourceFile:812)
	at eov.a(SourceFile:93)
	at net.minecraft.server.MinecraftServer.v(SourceFile:671)
	at net.minecraft.server.MinecraftServer.a(SourceFile:256)
	at net.minecraft.server.MinecraftServer$$Lambda$3957/239787403.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:745)