Tolerate null oid pointer in gss_release_oid()

Under some circumstances, gss_inquire_name() can call
gss_release_oid() with a null oid pointer, which currently causes a
null dereference.  The least invasive fix is for gss_release_oid() to
check for the invalid null pointer and return an error, like other
GSS-API functions do.

(cherry picked from commit 4676e823e6ee9a5731872b31c5588c1b5932e0a3)

https://github.com/krb5/krb5/commit/cda902bf6f4d1e18d541bf3705ae19f783effcae
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: cda902bf6f4d1e18d541bf3705ae19f783effcae
Branch: krb5-1.13
 src/lib/gssapi/mechglue/g_initialize.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)