Avoid a potential read overflow. This was not deemed a security issue by
upstream; it was fixed upstream comprehensively a few weeks ago in
77199d6ec8986d470487e66f8ea8f4cf43d2e20c.

PR: 200241
Patch by: Hanno Böck <hanno@hboeck.de>
Obtained from: http://www.openwall.com/lists/oss-security/2015/05/16/3