[MC-34708] NullPointerException thrown on cancelling when "Logging in..."

When logging in to the Snapshot server, if you press "Cancel" while it's at the "Logging in..." phase, a NullPointerException will be thrown.

Steps to recreate;
1. Join a snapshot server
2. While "Logging in..." press cancel

---- Minecraft Crash Report ----
// Quite honestly, I wouldn't worry myself about that.

Time: 10/10/13 10:53 AM
Description: Exception in server tick loop

java.lang.NullPointerException
	at mx.d(SourceFile:103)
	at mx.a(SourceFile:95)
	at mo.c(SourceFile:130)
	at net.minecraft.server.MinecraftServer.u(SourceFile:528)
	at lh.u(SourceFile:259)
	at net.minecraft.server.MinecraftServer.t(SourceFile:440)
	at net.minecraft.server.MinecraftServer.run(SourceFile:358)
	at kw.run(SourceFile:616)


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

-- System Details --
Details:
	Minecraft Version: 13w41a
	Operating System: Linux (amd64) version 2.6.32-358.18.1.el6.x86_64
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 1828113784 bytes (1743 MB) / 2137849856 bytes (2038 MB) up to 8580300800 bytes (8182 MB)
	JVM Flags: 10 total; -Xms2G -Xmx8G -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:ParallelGCThreads=2 -XX:+CMSParallelRemarkEnabled -XX:+DisableExplicitGC -XX:MaxGCPauseMillis=500 -XX:SurvivorRatio=16 -XX:TargetSurvivorRatio=90
	AABB Pool Size: 1707 (95592 bytes; 0 MB) allocated, 1444 (80864 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 1294 (72464 bytes; 0 MB) allocated, 581 (32536 bytes; 0 MB) used
	Player Count: 1 / 20; [mi['McMuffinn6'/3332, l='world', x=-472.33, y=106.00, z=226.09]]
	Is Modded: Unknown (can't tell)
	Type: Dedicated Server (map_server.txt)