Fix unlikely double free in PKINIT client code

In pa_pkinit_gen_req, if the cleanup handler is reached with non-zero
retval and non-null out_data, out_data is freed, then dereferenced,
then freed again.  This can only happen if one of the small fixed-size
malloc requests fails after pkinit_as_req_create succeeds, so it is
unlikely to occur in practice.

(cherry picked from commit cc002d6c1ccfc08356d01ba83e72a46855d0302c)

https://github.com/krb5/krb5/commit/32d98df8acbc7155b513142c8b6e5ce6b5fb78d8
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 32d98df8acbc7155b513142c8b6e5ce6b5fb78d8
Branch: krb5-1.11
 src/plugins/preauth/pkinit/pkinit_clnt.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)