[CM] Fix NPE due to unvalidated callback value

Fix flaky test resulting from the above fix.

Bug: 132950880
Test: atest ConnectivityServiceTest
Merged-In: Ia2cc04b42288ea987483e5ab0e0a10093dc49502
Change-Id: Ia2cc04b42288ea987483e5ab0e0a10093dc49502
(cherry picked from commit cc65a628eb1172dc7b942d7f51b702099c15c23b)
1 file changed