Merge "Fix crash in settings when no fingerprint is available"

src/com/android/settings/FingerprintUiHelper.java

@@ -56,9 +56,11 @@ public class FingerprintUiHelper extends FingerprintManager.AuthenticationCallba
     }
 
     public void stopListening() {
+        if (mCancellationSignal != null) {
             mCancellationSignal.cancel();
             mCancellationSignal = null;
         }
+    }
 
     private void setFingerprintIconVisibility(boolean visible) {
         mIcon.setVisibility(visible ? View.VISIBLE : View.GONE);