[MC-193073] Game crashes when Piglins or Piglin Brutes convert to Zombified Piglins

Piglins will crash the game when they convert to Zombified Piglins

Steps to recreate:
1. Spawn piglins using spawn egg in the overworld
2. Wait for them to convert
3. Crash

20w27a: crash-2020-07-01_12.22.14-server.txt

Description: Ticking entity

java.lang.NullPointerException: Ticking entity
	at bdf.b(SourceFile:100)
	at bdg.b(SourceFile:362)
	at bdg.N(SourceFile:349)
	at apb.dQ(SourceFile:741)
	at apa.k(SourceFile:2506)
	at apb.k(SourceFile:539)
	at bce.k(SourceFile:43)
	at apa.j(SourceFile:2252)
	at apb.j(SourceFile:339)
	at zb.a(SourceFile:617)
	at zb$$Lambda$4896/179971218.accept(Unknown Source)
	at bqk.a(SourceFile:603)
	at zb.a(SourceFile:407)
	at net.minecraft.server.MinecraftServer.b(SourceFile:873)
	at net.minecraft.server.MinecraftServer.a(SourceFile:813)
	at eph.a(SourceFile:92)
	at net.minecraft.server.MinecraftServer.v(SourceFile:672)
	at net.minecraft.server.MinecraftServer.a(SourceFile:256)
	at net.minecraft.server.MinecraftServer$$Lambda$4306/215680372.run(Unknown Source)
	at java.lang.Thread.run(Thread.java:745)