There is:

eZSys::init( 'webdav.php', $ini->variable( 'SiteAccessSettings', 'ForceVirtualHost' ) === 'true' );

should be:

$ini = eZINI::instance();
eZSys::init( 'webdav.php', $ini->variable( 'SiteAccessSettings', 'ForceVirtualHost' ) === 'true' );

$ini is not declared before, so webdav returns fatal error .