Add null check for clientInfo

If the binder death notification for a INsdManagerCallback was
received before any calls are received by NsdService, the
clientInfo would be cleared and cause NPE. Thus, add a null check
to prevent crash.

Bug: 241741274
Test: atest FrameworksNetTests
Change-Id: Iebe761cd579bf3ee46ead389620bed60a21e3154
2 files changed