Reduce gap above user list in multiuser settings.

This fixes a large gap above the user list, which occurred because
a PreferenceCategory was used for this with a blank title.

Bug: 224659273
Test: Install and inspect
Change-Id: I82c4491cc6a5111c6517b2845b44632e0859e1b6

src/com/android/settings/users/UserSettings.java

@@ -1102,6 +1102,7 @@ public class UserSettings extends SettingsPreferenceFragment
             mUserListCategory.setTitle(R.string.user_list_title);
         } else {
             mUserListCategory.setTitle(null);
+            mUserListCategory.setLayoutResource(R.layout.empty_view);
         }
 
         // Remove everything from mUserListCategory and add new users.