Basically we need to assure that the Contacts variable is declared because we are getting a ReferenceError in the imports cases when showing the contacts list and entering the search mode. Other options to get the same result could be:
   1) if (typeof Contacts !== 'undefined' && Contacts.navigation)...
   2) if ('Contacts' in window && Contacts.navigation)...
Once we know that the global Contacts variable is declared, I just avoided writing the "window." part again but if you feel more confortable we could go for:
   - if (window.Contacts && window.Contacts.navigation)...