Handle no IccRecords in updateSpnDisplay differently.

Rather than doing nothing in GsmServiceStateTracker#updateSpnDisplay
if mIccRecords is null, use a rule of 0 and an empty spn. And then keep the
remaining logic the same.

This allows "Emergency Only Calls" to be displayed in the lock and
notification screens if there is no SIM card.

Bug: 7276760
Change-Id: I0f969c8f5cad204e80c63d2e1a8e896cb7f4c02a