[MC-79757] Skull URLs with invalid filenames cause client to crash

This is related to ~~MC-79635~~ and was found during my testing for ~~MC-79756~~.

Upon sending an illegal url, such as http://minecon.mojang.com/images/sky.png## or http://textures.minecraft.net/texture/ca8caeacf97fabf2cd838ffe6b1e4cb0a41eea2cb2467a9f234a0dd703995## , the client crashes with the following error:

com.google.common.util.concurrent.UncheckedExecutionException: java.lang.IllegalArgumentException: Invalid URL 'http://minecon.mojang.com/images/sky.png##'
	at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2201)
	at com.google.common.cache.LocalCache.get(LocalCache.java:3934)
	at com.google.common.cache.LocalCache.getOrLoad(LocalCache.java:3938)
	at com.google.common.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:4821)
	at com.google.common.cache.LocalCache$LocalLoadingCache.getUnchecked(LocalCache.java:4827)
	at bnp.a(SourceFile:126)
	at bhk.a(SourceFile:76)
	at bfi.a(SourceFile:52)
	at bjh.a(SourceFile:122)
	at bjh.a(SourceFile:323)
	at bjh.b(SourceFile:359)
	at avo.a(SourceFile:880)
	at avo.a(SourceFile:336)
	at avo.a(SourceFile:144)
	at bfk.a(SourceFile:1021)
	at ave.av(SourceFile:914)
	at ave.a(SourceFile:325)
	at net.minecraft.client.main.Main.main(SourceFile:124)
Caused by: java.lang.IllegalArgumentException: Invalid URL 'http://minecon.mojang.com/images/sky.png##'
	at com.mojang.authlib.yggdrasil.YggdrasilMinecraftSessionService.isWhitelistedDomain(YggdrasilMinecraftSessionService.java:204)
	at com.mojang.authlib.yggdrasil.YggdrasilMinecraftSessionService.getTextures(YggdrasilMinecraftSessionService.java:149)
	at bnp$1.a(SourceFile:47)
	at bnp$1.load(SourceFile:44)
	at com.google.common.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3524)
	at com.google.common.cache.LocalCache$Segment.loadSync(LocalCache.java:2317)
	at com.google.common.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2280)
	at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2195)
	... 17 more