mvc: as previously seen PHP has trouble iterating over empty nodes

It feels like 2105 and is_array() -> isset() all over again...

src/opnsense/mvc/app/models/OPNsense/Base/Menu/MenuSystem.php

@@ -105,11 +105,14 @@ class MenuSystem
         }
         // add interfaces to "Interfaces" menu tab... kind of a hack, may need some improvement.
         $ifarr = array();
-        foreach (Config::getInstance()->object()->interfaces->children() as $key => $node) {
+        $config = Config::getInstance()->object();
+        if ($config->interfaces->count() > 0) {
+            foreach ($config->interfaces->children() as $key => $node) {
                 if (empty($node->virtual)) {
                     $ifarr[$key] = !empty($node->descr) ? (string)$node->descr : strtoupper($key);
                 }
             }
+        }
         natcasesort($ifarr);
         $ordid = 0;
         foreach ($ifarr as $key => $descr) {