[DO NOT MERGE] Update title for null uri when setting changes

Currently, the title will not update at all if set to silent.

Bug: 130445562
Test: make RunSettingsRoboTests -j48
Change-Id: Id8fc0182adb37c05436f5924b7dcdffb9d994e0d

src/com/android/settings/notification/RingtonePreferenceControllerBase.java

@@ -55,7 +55,7 @@ public abstract class RingtonePreferenceControllerBase extends AbstractPreferenc
 
         final CharSequence summary;
         if (ringtoneUri == null) {
-            summary = null;
+            summary = mContext.getString(com.android.internal.R.string.ringtone_silent);
         } else {
             summary = Ringtone.getTitle(
                     mContext, ringtoneUri, false /* followSettingsUri */, true /* allowRemote */);