Fix NPE crash in UsageAccessDetails

mPackageInfo will be null in RefreshUI method in UsageAccessDetails.java

Bug:https://issuetracker.google.com/issues/65872768
Test:As explained in the link above

Change-Id: I8bd4b822cfe5d8a3347ca7f5886605cbdfb9b8b6
Signed-off-by: tiansiming <tiansiming@xiaomi.com>

src/com/android/settings/applications/UsageAccessDetails.java

@@ -137,6 +137,9 @@ public class UsageAccessDetails extends AppInfoWithHeader implements OnPreferenc
 
     @Override
     protected boolean refreshUi() {
+        if (mPackageInfo == null) {
+            return false;
+        }
         mUsageState = mUsageBridge.getUsageInfo(mPackageName,
                 mPackageInfo.applicationInfo.uid);