Fix error "BigBlueButton\Core\Attendee::__construct(): Node no longer exists" if the $xml doesn't have the customdata property.

Author: davidrojo

src/Core/Attendee.php

@@ -80,8 +80,10 @@ public function __construct($xml)
         $this->hasVideo        = $xml->hasVideo->__toString() === 'true';
         $this->clientType      = $xml->clientType->__toString();
 
-        foreach ($xml->customdata->children() as $data) {
-            $this->customData[$data->getName()] = $data->__toString();
+        if ($xml->customdata) {
+            foreach ($xml->customdata->children() as $data) {
+                $this->customData[$data->getName()] = $data->__toString();
+            }
         }
     }