deleting a contact crashes app

[mwfarb]

Tested on iOS 8.3 and iOS 6.1.6. To reproduce:

1. In Messages tab, tap "+" button.
2. Swipe left on any contact and tap Delete.
3. Crash.

[mwfarb]

I should add, after restarting the app and logging in, to check if delete worked, the recipient is actually removed from the list. Tested on 1.8.2 development branch a4d10ce.

[mwfarb]

Production version 1.8.1 does not crash.

[tenmalin]

Close in ed23707