Solution proposal for issue #1647.

Avoid a memory alignment issue.

Signed-off-by: Matthias Kraft <Matthias.Kraft@softwareag.com>
CLA: trivial
Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1650)