Add TimeZoneProviderStatus' nullness check.

The mTimeZoneProviderStatus of TimeZoneProviderEvent will be null if it came from [1], and it will cause 'system_server' NPE in the method of 'preProcess'.

[1] https://cs.android.com/android/platform/superproject/main/+/main:frameworks/base/core/java/android/service/timezone/TimeZoneProviderService.java;l=205;drc=e13dc3f47bb058cda591ff7c4db38100f3a8276f



Bug:353886493

Test: atest core/tests/timetests/src/android/service/timezone/
Test: atest services/tests/timetests/src/com/android/server/timezonedetector/location/

Change-Id: Id3d467f72da0ad17388d7f6f3af649fce45e9af6
Signed-off-by: hupeng3 <hp121520@gmail.com>