Fixed -[ETWidgetLayout invocationForSelector:] on Mac OS X where +invocationWithMethodSignature: doesn't accept a nil argument
Fixed -[ETWidgetLayout invocationForSelector:] on Mac OS X where +invocationWithMethodSignature: doesn't accept a nil argument

git-svn-id: 0833b781a6984bca00fd44c5b8a33a6c879c84c9@4571 7b3f36aa-e6db-49c1-8b4c-66eac1997e64

etoile/EtoileUI,etoile/EtoileUI