Clear mGuestRestrictions before loading from disk

Only guest user restrictions that are set to true are saved in
writeUserListLP. When loading <guestRestrictions>, they are applied
on top of mGuestRestrictions filled with default values.
Restrictions set to false are reset and this was causing the issue.

Bug: 33250860
Test: Manual
Change-Id: I6e5c792a3adcf2116bb26fd5feba551d7edcb28e

services/core/java/com/android/server/pm/UserManagerService.java

@@ -1810,8 +1810,8 @@ public class UserManagerService extends IUserManager.Stub {
                             if (type == XmlPullParser.START_TAG) {
                                 if (parser.getName().equals(TAG_RESTRICTIONS)) {
                                     synchronized (mGuestRestrictions) {
-                                        mGuestRestrictions.putAll(
-                                                UserRestrictionsUtils.readRestrictions(parser));
+                                        UserRestrictionsUtils
+                                                .readRestrictions(parser, mGuestRestrictions);
                                     }
                                 }
                                 break;

services/core/java/com/android/server/pm/UserRestrictionsUtils.java

@@ -207,6 +207,7 @@ public class UserRestrictionsUtils {
     }
 
     public static void readRestrictions(XmlPullParser parser, Bundle restrictions) {
+        restrictions.clear();
         for (String key : USER_RESTRICTIONS) {
             final String value = parser.getAttributeValue(null, key);
             if (value != null) {