Fix -initWithScheme: crash

Sooooo, it turns out that -initWithScheme:host:path: will raise an NSInvalidArgumentException if path is not absolute.

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSURL initWithScheme:host:path:]: path is not absolute.'

And of course this is not documented. 

O_o

/remember AppKit
/remember Documentation or GTFO.