don't segfault when -nonat is used and nat_map reinit is called

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@16253 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/include/switch_nat.h

@@ -88,6 +88,10 @@ SWITCH_DECLARE(void) switch_nat_reinit(void);
  \param sticky make the mapping permanent
 */
 SWITCH_DECLARE(switch_status_t) switch_nat_add_mapping(switch_port_t port, switch_nat_ip_proto_t proto, switch_port_t *external_port, switch_bool_t sticky);
+/*!
+ \brief Has the NAT subsystem been initialized
+*/
+SWITCH_DECLARE(switch_bool_t) switch_nat_is_initialized(void);
 /*!
  \brief Deletes a NAT mapping
  \param proto Protocol