Fix the bug TM#getNetworkCountryISO returns null in SUW.

TM#getNetworkCountryISO() will pass INVALID_PHONE_INDEX if no default
SIM is ever set, and ends up having a null phone object. Then an
empty string is returned instead of proper value from LocaleTracker#
getCurrentCountry.

Bug: 111387352
Test: TelephonyManagerTestApp. With no SIM, call TM#getNetworkCountryISO
and see the result.
Change-Id: I2bf04620d58a9610b1b2ea53be193061350d0137
1 file changed