as the comment (which is removed now) said:

```
        XXX: This method is broken, since "total_size" field is not
        present in the listbox rendering any longer. It should be
        removed.
```

Also:
- make sure that Listbox always knows how many lines are to be displayed.
- add testPagerWithCustomListMethod in listbox_zuite of erp5_ui_test,
which checks that listbox jumping to previous/next/first/last works correctly
for a list method that returns only the elements that the listbox is to render.


/reviewed-on !776