Disable App data usage preference if there's no usage data.

- when there is no usage data at all, launching the app data usage page
will show something blank, as there's no cycle with available usage
data. Check the overall historic usage to make sure that there's
usage data to be shown, otherwise, disable the preference.

Fixes: 123518021
Test: make RunSettingsRoboTests
Change-Id: I2d19f85e8618c41e2c31b9e4259cdc522f69e371

src/com/android/settings/network/telephony/DataUsagePreferenceController.java

@@ -63,7 +63,16 @@ public class DataUsagePreferenceController extends TelephonyBasePreferenceContro
     @Override
     public void updateState(Preference preference) {
         super.updateState(preference);
-        final boolean enabled = mSubId != SubscriptionManager.INVALID_SUBSCRIPTION_ID;
+        if (mSubId == SubscriptionManager.INVALID_SUBSCRIPTION_ID) {
+            preference.setEnabled(false);
+            return;
+        }
+        long usageLevel = mDataUsageInfo.usageLevel;
+        if (usageLevel <= 0L) {
+            final DataUsageController controller = new DataUsageController(mContext);
+            usageLevel = controller.getHistoricalUsageLevel(mTemplate);
+        }
+        final boolean enabled = usageLevel > 0L;
         preference.setEnabled(enabled);
 
         if (enabled) {