Check for null before invoking finish()

Fixes: 124406109

Test: manual
Change-Id: Idee87c060ffd84395355ccdc5248166f1a6aeaf0

src/com/android/settings/biometrics/face/FaceSettings.java

@@ -58,7 +58,9 @@ public class FaceSettings extends DashboardFragment {
     private FaceSettingsAttentionPreferenceController mAttentionController;
 
     private final FaceSettingsRemoveButtonPreferenceController.Listener mRemovalListener = () -> {
+        if (getActivity() != null) {
             getActivity().finish();
+        }
     };
 
     public static boolean isAvailable(Context context) {