Processing of empty Station site name in 9M network

See StationXmlReaderMandatoryException in _run_site() method in ImporterStationXML12Station class.

By fdsn, site name is mandatory : https://stationxml-doc.readthedocs.io/en/release-1.1.0/reference.html#name-required

For now, this issue is handled by setting an empty string in site name. But it might be good to have a proper site name