Fix drawing on wxDC when using right-to-left layout in wxMSW.

Avoid integer overflow when setting wxDC scale. This affected (i.e. broke)
drawing in RTL but probably not only that.

Closes #16254.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@77022 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775