[MC-86490] Chunk not loaded caused by tamed dogs and cats with malformed OwnerUUIDs

When I loaded up a world from 15w32c into 15w33c there was a chunk loading error right in the middle of my base. The chunk had loaded as if it was a brand new map, freshly generated. It even had rabbits, which is not correct since the map is originally from 1.7. I've attached some screen shots showing the same area in 32c and 33c, also the server report from the terminal window.

_{Mod comment}
In 15w33c the UUID parser seems to be less lenient so that chunks containing tamed pets with broken OwnerUUIDs (caused by ~~MC-50339~~) won't load anymore.

[23:13:27] [Server thread/ERROR]: Couldn't load chunk
e: Loading entity NBT
	at qu.f(SourceFile:1319) ~[minecraft_server.jar:?]
	at qw.a(SourceFile:187) ~[minecraft_server.jar:?]
	at aqq.a(SourceFile:316) ~[minecraft_server.jar:?]
	at aqq.a(SourceFile:81) ~[minecraft_server.jar:?]
	at aqq.a(SourceFile:68) ~[minecraft_server.jar:?]
	at lj.e(SourceFile:125) [minecraft_server.jar:?]
	at lj.c(SourceFile:77) [minecraft_server.jar:?]
	at lh$a.<init>(SourceFile:39) [minecraft_server.jar:?]
	at lh.a(SourceFile:231) [minecraft_server.jar:?]
	at lh.a(SourceFile:263) [minecraft_server.jar:?]
	at md.a(SourceFile:233) [minecraft_server.jar:?]
	at md.c(SourceFile:285) [minecraft_server.jar:?]
	at md.a(SourceFile:140) [minecraft_server.jar:?]
	at lu.b(SourceFile:110) [minecraft_server.jar:?]
	at lu.c(SourceFile:56) [minecraft_server.jar:?]
	at ek.a(SourceFile:221) [minecraft_server.jar:?]
	at lr.c(SourceFile:168) [minecraft_server.jar:?]
	at net.minecraft.server.MinecraftServer.D(SourceFile:643) [minecraft_server.jar:?]
	at kt.D(SourceFile:299) [minecraft_server.jar:?]
	at net.minecraft.server.MinecraftServer.C(SourceFile:553) [minecraft_server.jar:?]
	at net.minecraft.server.MinecraftServer.run(SourceFile:457) [minecraft_server.jar:?]
	at java.lang.Thread.run(Thread.java:695) [?:1.6.0_65]
Caused by: java.lang.IllegalArgumentException: Invalid UUID string: 98f1a2155398401c81462eab72e6c0b5
	at java.util.UUID.fromString(UUID.java:201) ~[?:1.6.0_65]
	at rl.a(SourceFile:62) ~[minecraft_server.jar:?]
	at vn.a(SourceFile:130) ~[minecraft_server.jar:?]
	at qu.f(SourceFile:1310) ~[minecraft_server.jar:?]
	... 21 more