[MC-81405] Crash by spawning a head with skin url

Spawning a head with skin url; http://textures.minecraft.net/texture/a crashes clients.

Example:

Command

give @p skull 1 3 {display:{Name:"Whups, crashed"},SkullOwner:{Id:7617FFC6-9320-4EED-B937-4ED635282451,Properties:{textures:[{Value:e3RleHR1cmVzOntTS0lOOnt1cmw6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvYSJ9fX0=}]}}}

Crash

java.lang.StringIndexOutOfBoundsException: String index out of range: 2
	at java.lang.String.substring(Unknown Source)
	at bnp.a(SourceFile:65)
	at bnp.a(SourceFile:53)
	at bhk.a(SourceFile:78)