Clear mCurrentChallengeOwner when owner dies

Fixes: 167523869

Test: 1) enter face settings
      2) kill settings app (adb shell pkill -9 com.android.settings)
      3) enter password on lockscreen
      No crash observed
Change-Id: I20c9b2850e34c6e063e7cb25ee8e6934f0a86f29

services/core/java/com/android/server/biometrics/sensors/ClientMonitor.java

@@ -176,6 +176,9 @@ public abstract class ClientMonitor<T> extends LoggableMonitor implements IBinde
 
     // TODO(b/157790417): Move this to the scheduler
     void binderDiedInternal(boolean clearListener) {
+        Slog.e(TAG, "Binder died, owner: " + getOwnerString()
+                + ", operation: " + this.getClass().getName());
+
         if (isAlreadyDone()) {
             Slog.w(TAG, "Binder died but client is finished, ignoring");
             return;

services/core/java/com/android/server/biometrics/sensors/face/Face10.java

@@ -510,8 +510,15 @@ class Face10 implements IHwBinder.DeathRecipient {
             if (mCurrentChallengeOwner != null) {
                 Slog.w(TAG, "Current challenge owner: " + mCurrentChallengeOwner
                         + ", interrupted by: " + opPackageName);
+                final ClientMonitorCallbackConverter listener =
+                        mCurrentChallengeOwner.getListener();
+                if (listener == null) {
+                    Slog.w(TAG, "Null listener, skip sending interruption callback");
+                    return;
+                }
+
                 try {
-                    mCurrentChallengeOwner.getListener().onChallengeInterrupted(mSensorId);
+                    listener.onChallengeInterrupted(mSensorId);
                 } catch (RemoteException e) {
                     Slog.e(TAG, "Unable to notify challenge interrupted", e);
                 }
@@ -524,7 +531,7 @@ class Face10 implements IHwBinder.DeathRecipient {
                 @Override
                 public void onClientStarted(@NonNull ClientMonitor<?> clientMonitor) {
                     if (client != clientMonitor) {
-                        Slog.e(TAG, "scheduleGenerateChallenge, mismatched client."
+                        Slog.e(TAG, "scheduleGenerateChallenge onClientStarted, mismatched client."
                                 + " Expecting: " + client + ", received: " + clientMonitor);
                         return;
                     }