legacy: fix for static file handler
legacy: fix for static file handler

* Addresses issue with empty filename in legacy static file handler.

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

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