[5.2] mod_submenu php fixes (joomla#44320)

Author: peter1szalatnay

administrator/modules/mod_submenu/src/Menu/Menu.php

@@ -100,7 +100,9 @@ public static function preprocess($parent)
 
             // Exclude item with menu item option set to exclude from menu modules
             if ($itemParams->get('menu-permission')) {
-                @list($action, $asset) = explode(';', $itemParams->get('menu-permission'));
+                $parts  = explode(';', $itemParams->get('menu-permission'));
+                $action = $parts[0];
+                $asset  = $parts[1] ?? null;
 
                 if (!$user->authorise($action, $asset)) {
                     $parent->removeChild($item);