Fix possible NPE in FingerprintManager.

There's an unsafe use of a @Nullable reference in FingerprintManager.
Add null check.

Bug: 254465749
Test: Manually confirm device doesn't crash during boot.
Change-Id: I26da2e9a2af06e110367fc6f1127df4fddbcc678

core/java/android/hardware/fingerprint/FingerprintManager.java

@@ -1080,7 +1080,7 @@ public class FingerprintManager implements BiometricAuthenticator, BiometricFing
      */
     public boolean isPowerbuttonFps() {
         final FingerprintSensorPropertiesInternal sensorProps = getFirstFingerprintSensor();
-        return sensorProps.sensorType == TYPE_POWER_BUTTON;
+        return sensorProps == null ? false : sensorProps.sensorType == TYPE_POWER_BUTTON;
     }
 
     /**