documents: improvement of legacy filename handling
- Improves support in filenames with dashes - on legacy BibDocFile.
- Cherry-picked from 71c456134f44ed13f80e98f8447fd1de49e680cc.
Signed-off-by: Harris Tzovanakis <me@drjova.com>
Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>