FP name shouldn't be allowed to allow/display non-null names

Fixes: 37360324
Test: try to save an empty FP name
make sure it doesn't display the empty name

Change-Id: Ie81699abc0da9513e5173364e8ae969bbe195ac6

src/com/android/settings/fingerprint/FingerprintSettings.java

@@ -47,6 +47,7 @@ import android.text.SpannableString;
 import android.text.SpannableStringBuilder;
 import android.text.TextPaint;
 import android.text.style.URLSpan;
+import android.text.TextUtils;
 import android.util.AttributeSet;
 import android.util.Log;
 import android.view.View;
@@ -604,7 +605,9 @@ public class FingerprintSettings extends SubSettings {
 
         private void renameFingerPrint(int fingerId, String newName) {
             mFingerprintManager.rename(fingerId, mUserId, newName);
+            if (!TextUtils.isEmpty(newName)) {
                 mFingerprintsRenaming.put(fingerId, newName);
+            }
             updatePreferences();
         }