chassis.c: Fix the possible NULL pointer deference in chassis_cleanup().

If chassis_rec is NULL but chassis_private_rec is not, chassis_rec->name
is a NULL pointer deference. This patch fixes it.

Fixes: 4adc10f ("Avoid nb_cfg update notification flooding")
Acked-by: Numan Siddique <numans@ovn.org>
Signed-off-by: Han Zhou <hzhou@ovn.org>

controller/chassis.c

@@ -843,7 +843,8 @@ chassis_cleanup(struct ovsdb_idl_txn *ovnsb_idl_txn,
     if (ovnsb_idl_txn) {
         ovsdb_idl_txn_add_comment(ovnsb_idl_txn,
                                   "ovn-controller: unregistering chassis '%s'",
-                                  chassis_rec->name);
+                                  chassis_rec ? chassis_rec->name
+                                  : chassis_private_rec->name);
         if (chassis_rec) {
             sbrec_chassis_delete(chassis_rec);
         }