Tolerate null oid pointer in gss_release_oid()

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.

ticket: 8201 (new)
target_version: 1.13.3
tags: pullup