D-Bus: Make the CurrentAuthMode property getter more robust

Now that mesh sets wpa_s->wpa_state = WPA_COMPLETED, it looks like this
getter can get called with wpa_s->current_ssid = NULL. That could result
in NULL pointer dereference, so need to protect that specific case.

Signed-off-by: Jouni Malinen <j@w1.fi>

wpa_supplicant/dbus/dbus_new_handlers.c

@@ -3228,9 +3228,11 @@ dbus_bool_t wpas_dbus_getter_current_auth_mode(
 			    "EAP-%s", eap_mode);
 		auth_mode = eap_mode_buf;
 
-	} else {
+	} else if (wpa_s->current_ssid) {
 		auth_mode = wpa_key_mgmt_txt(wpa_s->key_mgmt,
 					     wpa_s->current_ssid->proto);
+	} else {
+		auth_mode = "UNKNOWN";
 	}
 
 	return wpas_dbus_simple_property_getter(iter, DBUS_TYPE_STRING,