Fix: contacts without emails and phones caused an error.
Fix: contacts without emails and phones caused an error.

The solution was to stop Contact.addToField() if the added DC object
did not have at least a non-empty property.

The problem was reported in #56 by @baatochan.

GioBonvi/GoogleContactsEventsNotifier,rowanthorpe/GoogleContactsEventsNotifier,baatochan/GoogleContactsEventsNotifier