cryptnet: Specify half of the remaining timeout for each CRL if CERT_VERIFY_REV_ACCUMULATIVE_TIMEOUT_FLAG was specified.

Instead of wasting the whole timeout on the first CRL.
Signed-off-by: Zebediah Figura <zfigura@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>