After a fresh install, an existing local volume can't be opened

[enzomich]

After a fresh install, attempts to open an existing volume in local storage fail: the volume is not seen, and no file chooser is presented to the user. However, if a dummy volume is created, the app asks for permission to access local storage, and after this is granted ANY existing volume can be opened. This suggests that the local storage access permission should be requested also before opening an existing volume, not only before creating one: that would fix the bug.