widget: Fix rendering issues with CSD on Windows
widget: Fix rendering issues with CSD on Windows

Replace GDK_WINDOW_HWND by gdk_win32_window_get_impl_hwnd() which gets
the HWND directly, without any side effects.

Related:
https://bugzilla.redhat.com/show_bug.cgi?id=1352216

Acked-by: Fabiano Fidêncio <d95e9796398a6087d3fb67947e5776c26b264733@fidencio.org>

flexVDI/spice-gtk,flexVDI/spice-gtk,fgouget/spice-gtk,fgouget/spice-gtk,fgouget/spice-gtk