Let user immediately save to device account when no accounts exist

ContactEditorFragment expects an account to be returned from the
activity otherwise it just closes, so save and pass the default
through if the user pressed cancel.

Test: Manually verified hitting cancel sets the device account as
the default and you're immediately taken to the editor without
needing to tap add contact again.

Bug: 34623569
Change-Id: I153af7cc89738fd80b7315b921d561723feb936d