Fix Settings crash when activity is null

in ManageApplications, if getActivity is null, it will cause crash
because in HelpUtils#prepareHelpMenuItem it will call activity's
getString method.

Test: manual
Change-Id: I4c9cf985e94192a936d195ea4279ec1d0f22eb10
Signed-off-by: songkailun <songkailun@xiaomi.com>

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

@@ -651,7 +651,11 @@ public class ManageApplications extends InstrumentedPreferenceFragment
 
     @Override
     public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
-        HelpUtils.prepareHelpMenuItem(getActivity(), menu, getHelpResource(), getClass().getName());
+        final Activity activity = getActivity();
+        if (activity == null) {
+            return;
+        }
+        HelpUtils.prepareHelpMenuItem(activity, menu, getHelpResource(), getClass().getName());
         mOptionsMenu = menu;
         inflater.inflate(R.menu.manage_apps, menu);
         updateOptionsMenu();