[MC-129517] Game crashes while loading chunks with player heads

I have a superflat world, where i have a chest with some player heads. When i try to load the world in 18w01a+ snapshots, the game crashes once it loads the chunk with this chest! Please fix this!

it's the same in 18w20a

Description: Rendering Block Entity

i: Non [a-z0-9/._-] character in path of location: minecraft:skins/Failboat
	at oh.<init>(SourceFile:36)
	at oh.<init>(SourceFile:41)
	at czd.a(SourceFile:61)
	at czd.a(SourceFile:57)
	at crf.a(SourceFile:134)
	at crf.a(SourceFile:83)
	at crf.a(SourceFile:63)
	at crf.a(SourceFile:26)
	at cqw.a(SourceFile:148)
	at cqw.a(SourceFile:128)
	at cow.a(SourceFile:684)
	at coq.b(SourceFile:1004)
	at coq.a(SourceFile:913)
	at coq.a(SourceFile:774)
	at cbf.b(SourceFile:823)
	at cbf.a(SourceFile:384)
	at net.minecraft.client.main.Main.main(SourceFile:141)