This addresses a bug where popover menus in the titlebar were rendered
only after a 2nd click. The first click was creating the View which the
second one then rendered.
In addition to this, `PopoverMenu::menu` function argument can now
return an `Option<View<T>>` instead of `View<T>` as the creation of the
menu can fail (as it might in case of git popover).

Release Notes:

- N/A