IO: fix unexpected MouseSouce type in AddMousePosEvent and AddMouseButtonEvent.

[RickHuang2001]

This is a PR to fix unexpected MouseSouce type in AddMousePosEvent and AddMouseButtonEvent.

Hi, ocornut.

I've been using segross/UnrealImGui for implementing in-game dev tools for a long time. Because of some issues on touch screen devices, I upgraded the ImGui Library to the latest version for the convience of ImGuiMouseSource_TouchScreen.

However, in the AddMousePosEvent and AddMouseButtonEvent, unexpected MouseSouce type was used, so it didn't work well.

[ocornut]

Wow, thanks for finding this!
AFAIK although semantically very incorrect, this would not have any side-effects with typical compiler alignments settings, as the MouseSource value of all three unions would align to the same location.

Did your setup use non-default struct packing? You can use offsetof() to tell the offset of all three variations of MouseSource.

I have pushed as a6857ed with minor amends (debug log prints also used the wrong union).

[RickHuang2001]

Thanks, ocornut. It's right that this can work with the same alignment!

Yesterday I edited a few other lines of codes at the same time in UnrealImGui Plugin, and it started to function correctly, so I didn't notice that I don't need changing the variation of MouseSource to make it work.