Handle null for the return of getCrossProfileCalendarPackages.

The return value of this API could be null after our decision for
API change as in b/121179845.

Bug: 121179845
Test: make ROBOTEST_FILTER=CrossProfileCalendarPreferenceControllerTest -j40 RunSettingsRoboTests
Change-Id: I834ccf83ecca8959d95288ac4fa1473d12eabfca
1 file changed