Possible memory leak on listview hover event

[ThibaudMZN]

While hovering items quickly in a listview, CPU memory goes up before eventually triggering a garbage collection

[ThibaudMZN]

This behavior can be fixed by caching the final image to draw than dispose it, the "leak" seems to come from this part.

[ThibaudMZN]

I've created a pull request to fix this issue. #246