[MC-160865] Waking up from a bed can cause the server to crash in specific circumstances

Title

The original title of this ticket was "Sleeping under the end portal crashes the game". It has been changed in order to prevent it from being leaked in the changelog.

The bug

If you sleep below an end portal, the server will crash if you wake up and are immediately teleported to the end (i.e., you're waking up inside of the portal blocks). This seems to be a regression of ~~MC-120567~~.

To reproduce

Find or build an end portal
Activate it
Place a bed one block below the portal
Sleep in the bed
→ The server will crash as soon as you wake up

Video

https://youtu.be/y3v9Eek8jgc

Crash report

1.14.4: crash-2019-09-11_11.26.25-server.txt

Description: Exception ticking world

java.util.ConcurrentModificationException
	at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1380)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502)
	at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
	at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
	at vk.a(SourceFile:304)
	at net.minecraft.server.MinecraftServer.b(SourceFile:835)
	at net.minecraft.server.MinecraftServer.a(SourceFile:774)
	at eac.a(SourceFile:128)
	at net.minecraft.server.MinecraftServer.run(SourceFile:642)
	at java.lang.Thread.run(Thread.java:745)