fixup! fix(userstatus): CALL status should overwrite MEETING status

apps/dav/lib/CalDAV/Status/StatusService.php

@@ -125,7 +125,7 @@ public function processCalendarStatus(string $userId): void {
  }
 
  // Only update the status if it's neccesary otherwise we mess up the timestamp
- if($currentStatus->getMessageId() !== IUserStatus::MESSAGE_CALENDAR_BUSY) {
+ if($currentStatus !== null && $currentStatus->getMessageId() !== IUserStatus::MESSAGE_CALENDAR_BUSY) {
  // One event that fulfills all status conditions is enough
  // 1. Not an OOO event
  // 2. Current user status (that is not a calendar status) was not set after the start of this event