fix(card): use accessor for createdAt in VTODO serialization

CardDetails extends Card and keeps its own default entity properties. Direct property access can therefore read null from the wrapper while the magic getter delegates through __call() to the inner Card.

That can crash any code path serializing a Card-like object with a due date via getCalendarObject(), not only CalDAV PUT handling.

Signed-off-by: Jaggob <37583151+Jaggob@users.noreply.github.com>

Author: Jaggob

lib/Db/Card.php

@@ -136,7 +136,7 @@ public function getCalendarObject(): VCalendar {
 		$event->UID = 'deck-card-' . $this->getId();
 		if ($this->getDuedate()) {
 			$creationDate = new DateTime();
-			$creationDate->setTimestamp($this->createdAt);
+			$creationDate->setTimestamp($this->getCreatedAt());
 			$event->DTSTAMP = $creationDate;
 			$event->DUE = new DateTime($this->getDuedate()->format('c'), new DateTimeZone('UTC'));
 		}