Handle unexpected case when TimeResult is null

Handle unexpected case when TimeResult is null during tests. This should
not be possible but theoretically NtpTrustedTime.getCachedTimeResult()
can return null so this is being done to keep any linter / null checker
happy.

Test: treehugger only
Bug: 271975153
Change-Id: I030fa268a83d1015213e6fc2cb6a8d804e74f7c0