fingerprint: hide link icon when there's no link

Test: verify fingerprint setup doesn't have link icon without a link.
Change-Id: I040500615815ffe9256089a9bc11b07da783fa79

res/layout/fingerprint_enroll_introduction.xml

@@ -190,6 +190,7 @@
             </LinearLayout>
 
             <LinearLayout
+                android:id="@+id/layout_footer_learn_more"
                 android:layout_width="match_parent"
                 android:layout_height="wrap_content"
                 android:orientation="horizontal">

src/com/android/settings/biometrics/fingerprint/FingerprintEnrollIntroduction.java

@@ -28,6 +28,7 @@ import android.hardware.fingerprint.FingerprintSensorPropertiesInternal;
 import android.os.Bundle;
 import android.text.Html;
 import android.text.method.LinkMovementMethod;
+import android.text.TextUtils;
 import android.util.Log;
 import android.view.View;
 import android.widget.ImageView;
@@ -161,6 +162,10 @@ public class FingerprintEnrollIntroduction extends BiometricEnrollIntroduction {
                 getNextButton().setEnabled(true);
             }));
         }
+
+        if (TextUtils.isEmpty(footerLink.getText())) {
+            findViewById(R.id.layout_footer_learn_more).setVisibility(View.GONE);
+        }
     }
 
     @Override