mod_session_crypto: Protect ourselves against underlying libraries who

fail to load without providing an error message of their own.

Submitted by: minfrin
Backported by: minfrin
Reviewed by: minfrin, sf, rjung

Backport of r1418655 from turnk.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1420072 13f79535-47bb-0310-9956-ffa450edef68