- minor refactoring to avoid deleting the first ("Custom") menuitem
of the resolver menulist. It is the first item that is selected when
popup opens and deleting it confuses keyboard navigation, so that
arrowDown/Up won't navigate the menu (unless the menu is hovered
over with a mouse)
- explicitly re-select the first item when the menulist closes.
Otherwise, in case of having navigated the menus with arrows
without changing selection and closing the popup, next time
resolver selector appears, arrowUp/Down will not navigate the list.
Only occurs on Windows.
- clear the resolver menus (except for the 1st item) when the popup closes
so that arrowUp/Down on focused dropdown don't select invalid
top-level menus (e.g. "North America").
- make sure that if the URL has been edited, the resolver dropdown's
value will switch to "Custom" even if the resolvers were not loaded
fixes: #4491
