Check for race condition between onAuthenticated and taskStackChanged

Bug: 111461540

Test: no more logs like the ones below

Change-Id: I784ecc71df1028bac8e0203156f79157f0509636
FingerprintService: onAuthenticated(owner=com.android.settings, id=-1049244503
FingerprintService: Stopping background authentication, top: com.example.android.biometric currentClient: com.android.settings
FingerprintService: client com.android.settings is no longer authenticating
FingerprintService: Done with client: com.android.settings
FingerprintService: handleError(client=null, error = 5)