Assign the char field separately.

Reported by MinGW GCC 10 with -Woverflow.
Signed-off-by: Rémi Bernon <rbernon@codeweavers.com>
Signed-off-by: Piotr Caban <piotr@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>