[MC-160248] Slime and magma cube spawners crash the game

The bug

When you put a slime egg into a spanner, it crashes your game, and when you try to get on the same world, it crashes the game until you break it.

How to reproduce

/give @s minecraft:spawner
/give @s minecraft:slime_spawn_egg
Place down the spawner
Right click it with the spawn egg
→ Game crashes

Crash report

19w35a: crash-2019-09-02_03.56.07-client.txt

Description: Rendering Block Entity

java.lang.IllegalArgumentException: Attribute is already registered!
	at akr.b(SourceFile:29)
	at akt.b(SourceFile:30)
	at awf.a(SourceFile:89)
	at awf.a(SourceFile:341)
	at bib.d(SourceFile:256)
	at drb.a(SourceFile:20)
	at drb.a(SourceFile:15)
	at drb.a(SourceFile:10)
	at dqq.a(SourceFile:139)
	at dqq.a(SourceFile:121)
	at dow.a(SourceFile:606)
	at dos.b(SourceFile:840)
	at dos.a(SourceFile:747)
	at dos.a(SourceFile:613)
	at czq.e(SourceFile:941)
	at czq.b(SourceFile:402)
	at net.minecraft.client.main.Main.main(SourceFile:194)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Thread: Render thread
Stacktrace:
	at akr.b(SourceFile:29)
	at akt.b(SourceFile:30)
	at awf.a(SourceFile:89)
	at awf.a(SourceFile:341)
	at bib.d(SourceFile:256)
	at drb.a(SourceFile:20)
	at drb.a(SourceFile:15)
	at drb.a(SourceFile:10)

-- Block Entity Details --
Details:
	Name: minecraft:mob_spawner // bwb
	Block: Block{minecraft:spawner}
	Block location: World: (-53,63,0), Chunk: (at 11,3,0 in -4,0; contains blocks -64,0,0 to -49,255,15), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Block: Block{minecraft:spawner}
	Block location: World: (-53,63,0), Chunk: (at 11,3,0 in -4,0; contains blocks -64,0,0 to -49,255,15), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Stacktrace:
	at dqq.a(SourceFile:139)
	at dqq.a(SourceFile:121)
	at dow.a(SourceFile:606)
	at dos.b(SourceFile:840)
	at dos.a(SourceFile:747)