macosx: Fix issues with initial state of library window navigation stack
This PR tackles two bugs with the navigation stack:
- Navigation buttons being incorrectly enabled on initial window load, when no navigation has taken place
- The restoration of the library window state incorrectly setting the navigation state for the library window navigation stack (dual entries, some not being correctly entered)
Signed-off-by: Claudio Cambra claudio.cambra@gmail.com