Some window procedures don't actually erase background when WM_ERASEBKGND is received. So when drawing
transparent buttons on such windows, there may be left over content from buttons of different states.
This commit adds a white background to all the button parts that shouldn't be transparent.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=52433Signed-off-by: Zhiyi Zhang <zzhang@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>