Improve `PecuniaDB` initialization to handle errors gracefully

Right now, it returns

Future.error(
        Exception('Attempted to open database without a logged in user'),
        StackTrace.current,
      ),

Which probably works just fine, but if an error occurs, it isn't handled properly. This should be handled in EntryScreen, LoginScreen and RegisterScreen where the database connection would be opened.

Deed

[ ] EntryScreen
[ ] LoginScreen
[ ] RegisterScreen

nazrinharris / pecunia

Improve `PecuniaDB` initialization to handle errors gracefully #147

Deed