Fix memory leak in SPNEGO initiator

If we eliminate a mechanism from the initiator list because
gss_init_sec_context fails, free the memory for that mech OID before
removing it from the list.

[ghudson@mit.edu: clarified commit message]

ticket: 7803 (new)
target_version: 1.12.1
tags: pullup

src/lib/gssapi/spnego/spnego_mech.c

@@ -890,6 +890,7 @@ init_ctx_call_init(OM_uint32 *minor_status,
 	 * can do this with recursion.  If all mechanisms produce errors, the
 	 * caller should get the error from the first mech in the list.
 	 */
+	gssalloc_free(sc->mech_set->elements->elements);
 	memmove(sc->mech_set->elements, sc->mech_set->elements + 1,
 		--sc->mech_set->count * sizeof(*sc->mech_set->elements));
 	if (sc->mech_set->count == 0)