[fix] springer: unsupported operand type(s) for +: 'NoneType' and 'str'

- fix issue reported #1809
- filter out `None` value from issn and isbn list
- add comments (from publicationName)
- add publisher

Closes: https://github.com/searxng/searxng/issues/1809


Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>