Notifier: Fix condition variable race.
Notifier: Fix condition variable race.

robotdotnet/ntcore,333fred/ntcore,wpilibsuite/ntcore,robotdotnet/ntcore,333fred/ntcore,333fred/ntcore,robotdotnet/ntcore,333fred/ntcore,robotdotnet/ntcore,wpilibsuite/ntcore,wpilibsuite/ntcore,wpilibsuite/ntcore