fix xPath not being optional in libvirt_storagepool_get_xml_desc()
fix xPath not being optional in libvirt_storagepool_get_xml_desc()

KnightSwarm/libvirt-php,KnightSwarm/libvirt-php,KnightSwarm/libvirt-php,KnightSwarm/libvirt-php,KnightSwarm/libvirt-php