CP try to fix "noe no longer exists" when calling isEnabled

src/opnsense/mvc/app/models/OPNsense/CaptivePortal/CPClient.php

@@ -115,11 +115,14 @@ class CPClient
     public function isEnabled()
     {
         $enabled_zones = 0 ;
-        foreach ($this->config->object()->captiveportal->children() as $cpzonename => $zone) {
+        $conf = $this->config->object();
+        if (isset($conf->captiveportal)) {
+            foreach ($conf->captiveportal->children() as $cpzonename => $zone) {
                 if (isset($zone->enable)) {
                     $enabled_zones++;
                 }
             }
+        }
 
         if ($enabled_zones > 0) {
             return true;