In case of error, XSetICValues() must return the first argument
that failed to be set.

But in some error paths, it returns False, which is converted to NULL,
so the function returns OK in case of error.
Signed-off-by: Yann Droneaud <yann@droneaud.fr>
Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>