[MC-123021] Crash on open if "Saves" is a link

The bug

Minecraft no longer starts if "saves" folder is a link as it tries to create it and an exception occurs, making the game crash.

Note: I use this "trick" to share games between Windows and Linux platform.

Crash report

17w48a: crash-2017-12-05_10.40.04-client.txt

Description: Initializing game

java.lang.RuntimeException: java.nio.file.FileAlreadyExistsException: /home/alain/.minecraft/saves
	at bix.<init>(SourceFile:36)
	at biu.<init>(SourceFile:38)
	at bmm.an(SourceFile:450)
	at bmm.a(SourceFile:366)
	at net.minecraft.client.main.Main.main(SourceFile:134)
Caused by: java.nio.file.FileAlreadyExistsException: /home/alain/.minecraft/saves
	at sun.nio.fs.UnixException.translateToIOException(UnixException.java:88)
	at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:102)
	at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:107)
	at sun.nio.fs.UnixFileSystemProvider.createDirectory(UnixFileSystemProvider.java:384)
	at java.nio.file.Files.createDirectory(Files.java:674)
	at java.nio.file.Files.createAndCheckIsDirectory(Files.java:781)
	at java.nio.file.Files.createDirectories(Files.java:727)
	at bix.<init>(SourceFile:33)
	... 4 more