Disable Enhanced notifications setting when default NAS is not available

Test: NotificationAssistantPreferenceControllerTest
Bug: 251400808
Change-Id: Idec520013bea32cfaea0285f33c525a6e37f0124
(cherry picked from commit 873b8544e1cd3eac6b994c3ef67721cdd8441b5b)
2 files changed