Add new issues for py-lmdb (CVE-2019-1622{4,5,6,7,8)

Mark those as undetermned for now. Apparently upstream was not notified
about the issues, cf.
https://github.com/jnwatson/py-lmdb/issues/210#issuecomment-531004224 .

Wait for upstream investigation on
https://github.com/jnwatson/py-lmdb/issues/210 .