Assert related to SetCursorPos fires in Demo app

[Damon3000s]

While running the Demo project there are asserts from ImGui.NET about SetCursorPos being used incorrectly. This was recently introduced when the ImGui.NET dependency was updated.

The assert is: "Code uses SetCursorPos()/SetCursorScreenPos() to extend window/parent boundaries. Please submit an item e.g. Dummy() to validate extent."

The code can be found here: https://github.com/ocornut/imgui/blob/master/imgui.cpp#L10084
The linked issue ca be found here: ocornut/imgui#5548

[Damon3000s]

I believe the issue is how the grid advances the cursor. It always advances to the top left of the next cell for drawing the content but I think it also advances one more time even after the final cell has been drawn. This is what I will investigate first.

[matt-edmondson]

Fixed by #161