Fix the track bar of Mupen64-RR-Lua input window having black background. Mupen64-RR-Lua doesn't actually handle
WM_ERASEBKGND even though it returns nonzero. And tests show that only WM_CTLCOLORSTATIC is sent when drawing themed
trackbar background.
Signed-off-by: Zhiyi Zhang <zzhang@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>