Fix Automatic time zone not working when no NITZ received.

When there is no NITZ time zone received from NW. Device will use unique
time zone by NW MCC Country ISO. In fixTimeZone method, if no NITZ time
zone received, saveNitzTimeZone method should not be called. Otherwise,
time zone will be fixed to system default time zone and cannot update by
Country ISO.

Test: Build pass.
Test: No NITZ received, time zone can be updated by NW MCC Country ISO.

Change-Id: I3e29f6c262825ea7a17915c988afec6d596d4570