session: fix commit after automatic table creation
session: fix commit after automatic table creation

* Fixes `commit()` call on database session object.  (PR #2265)

Reviewed-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

inveniosoftware/invenio,tiborsimko/invenio,inveniosoftware/invenio,tiborsimko/invenio