legacy: BibIndex timestamp fix
legacy: BibIndex timestamp fix

* FIX Changes the default timestamp to a valid datetime value when
  reindexing via `-R`.

Reviewed-by: Jan Aage Lavik <8d55e006a1b29770f275a5c59a7341f17f8e69d5@cern.ch>
Signed-off-by: Javier Martin Montull <ea6b80e26c65acc242d8916fb6eefa01b123cb69@cern.ch>

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