Don't use SMS database until after the phone is unlocked

When the device is encrypted and a passcode is set,
the SMS database isn't available and the MAP service
crashes when trying to access it. The service will now
respond with OBEX_SERVICE_UNAVAILABLE until the phone
is unlocked. At this point, the SMS database will
notify the content observer that all the messages are
available, and send corresponding events.

Bug: 29990836
Change-Id: I53f12d0e114212d94f16b56df7c7dbe73f6254df