Fix NPE of UnrestrictedDataAccessPreference

Add null check for the DataUsageState to avoid NPE since it comes from
the extraInfo of AppEntry that possibly be null.

Fixes: 217250071
Test: manual
Change-Id: I1a41a49ed74bc6addc6b5dd0564973c210a6af74

src/com/android/settings/datausage/UnrestrictedDataAccessPreference.java

@@ -88,7 +88,7 @@ public class UnrestrictedDataAccessPreference extends AppSwitchPreference implem
 
     @Override
     protected void onClick() {
-        if (mDataUsageState.isDataSaverDenylisted) {
+        if (mDataUsageState != null && mDataUsageState.isDataSaverDenylisted) {
             // app is denylisted, launch App Data Usage screen
             AppInfoDashboardFragment.startAppInfoFragment(AppDataUsage.class,
                     R.string.data_usage_app_summary_title,