[MC-107559] Totem of undying crashing game when using instant damage pot(only when used by commands).

Put the summary of the bug you're having here
Totem of undying crashing game when using instant damage pot(only when used by commands).
What I expected to happen was...:

So i was playing around with totem of undying and command blocks and i used the following command while having totem in my off hand:
/effect @a minecraft:instant_damage. I repeated the command 3 times so i had 1 heart left. I executed the command again, expecting that totem will save me from dying but it didnt. My minecraft crashed. I tried it 3 times more and same resoult every time. Here is the crash report log:

---- Minecraft Crash Report ----
// This is a token for 1 free hug. Redeem at your nearest Mojangsta: [~~HUG~~]

Time: 28.9.2016 20:38
Description: Ticking player

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.remove(HashMap.java:1443)
	at sr.bO(SourceFile:514)
	at sr.U(SourceFile:309)
	at si.A_(SourceFile:351)
	at sr.A_(SourceFile:1616)
	at aat.A_(SourceFile:271)
	at lx.k_(SourceFile:282)
	at mh.F_(SourceFile:179)
	at er.a(SourceFile:232)
	at mg.c(SourceFile:187)
	at net.minecraft.server.MinecraftServer.D(SourceFile:652)
	at net.minecraft.server.MinecraftServer.C(SourceFile:562)
	at cby.C(SourceFile:154)
	at net.minecraft.server.MinecraftServer.run(SourceFile:466)
	at java.lang.Thread.run(Thread.java:745)


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

-- Head --
Thread: Server thread
Stacktrace:
	at java.util.HashMap$HashIterator.remove(HashMap.java:1443)
	at sr.bO(SourceFile:514)
	at sr.U(SourceFile:309)
	at si.A_(SourceFile:351)
	at sr.A_(SourceFile:1616)
	at aat.A_(SourceFile:271)

-- Player being ticked --
Details:
	Entity Type: null (lx)
	Entity ID: 0
	Entity Name: Matic2000
	Entity's Exact location: 11,50, 4,00, 12,14
	Entity's Block location: World: (11,4,12), Chunk: (at 11,0,12 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Entity's Momentum: 0,00, -0,08, 0,00
	Entity's Passengers: []
	Entity's Vehicle: ~~ERROR~~ NullPointerException: null
Stacktrace:
	at lx.k_(SourceFile:282)
	at mh.F_(SourceFile:179)
	at er.a(SourceFile:232)

-- Ticking connection --
Details:
	Connection: er@5f34c7e7
Stacktrace:
	at mg.c(SourceFile:187)
	at net.minecraft.server.MinecraftServer.D(SourceFile:652)
	at net.minecraft.server.MinecraftServer.C(SourceFile:562)
	at cby.C(SourceFile:154)
	at net.minecraft.server.MinecraftServer.run(SourceFile:466)
	at java.lang.Thread.run(Thread.java:745)

-- System Details --
Details:
	Minecraft Version: 16w39a
	Operating System: Windows 8.1 (amd64) version 6.3
	Java Version: 1.8.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 137472280 bytes (131 MB) / 375955456 bytes (358 MB) up to 1060372480 bytes (1011 MB)
	JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Player Count: 1 / 8; [lx['Matic2000'/0, l='Test', x=11,50, y=4,00, z=12,14]]
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.

Steps to Reproduce:
1. Get totem of undying in your off hand slot
2.Type command: /effect @p instant_damage
3. Repeat until death
4.Watch the game crash
5.Fix the bug.