Fixed widgets not being updated in BoxLayout when a child widget's index was changed using setWidgetIndex (fixes #202)

[CasualYT31]

Previously, when a widget within a BoxLayout-derived container (HorizontalLayout, VerticalLayout, HorizontalWrap) had its index changed via Container::setWidgetIndex(), it would not update the widgets in the BoxLayout using updateWidgets(). This would cause the widget to appear not to have been assigned a new index, until updateWidgets() was called in some other way (for example, when the BoxLayout gained a new widget, or if the BoxLayout was resized).

Now, Container::setWidgetIndex() is virtual, and BoxLayout overrides it. The overridden implementation invokes Container::setWidgetIndex(), and returns the result of the call. If the result of that call is true, the index change was successful, so updateWidgets() is called to show the change in the index immediately.

[texus]

Thanks for the detailed information and the PR with a fix.

One minor detail: the using Container::setWidgetIndex; line isn't needed. I assume you added it because it was used on other overridden functions in BoxLayout, but it is only needed in a special case. If the base class contains multiple functions with the same name (but with different parameters), and only one of them is overridden, then the others would become hidden. The using line makes it such that you can still call both the overridden (e.g. setSize(Layout2d)) and non-overridden (e.g. setSize(Layout, Layout)) functions. There is only one setWidgetIndex function, so it doesn't apply here and the using line has no effect.