QCocoaMenu: return YES if we have a shortcut for a pseudo-first responder

When running a modal session with NSOpenPanel (QFileDialog), our menu delegate
should not touch qApp->focusObject, since it's not what actually has focus
inside NSOpenPanel (will be some native view). Return YES instead.

Task-number: QTBUG-17291
Change-Id: I94f3281237fb25495d317b02310bf9d77b21d2ba
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>