update fallback logic to use cached country

Existing code only falls back to cached location when service state
is POWER_OFF. There can be race conditions when LocaleTracker updates
country iso to NULL, but service state tracker still has not updated
its state to POWER_OFF.

This change is to always fallback to cached locale if current locale is
not available.

Bug: 282712991
Test: atest and b2b calls
Change-Id: I5168a1e118768bb315601591ee31a5e799ff240d