GDI: Scrolling does not work for list view

Using the GDI implementation that came with the demo, the scrollbars don't seem to work 100% on list view objects. The bar can be moved up and down, but it doesn't offset the content inside.

I've made sure that the `nk_list_view` variable I made is outside my while loop, and that GDI has the ability to properly scroll with main windows.

Start by reproducing the issue with the GDI implementation from the demo and a persistent nk_list_view variable outside the loop. Trace the list view scrollbar behavior and verify that moving the scrollbar offsets the content inside list view objects, while confirming that main-window scrolling still works.

Written by the indexing model from the issue text.