MonitorFromWindow() may return a different monitor if switching to a
smaller display mode.

Fix Railroad Tycoon II crashes.
Signed-off-by: Zhiyi Zhang <zzhang@codeweavers.com>
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>