Fix language Vs field treatment in create_searchwithin_selection_box.
Fix language Vs field treatment in create_searchwithin_selection_box.

tiborsimko/invenio-records,tiborsimko/invenio-search,inveniosoftware/invenio-search,inveniosoftware/invenio-records,tiborsimko/invenio-records,inveniosoftware/invenio-search,inveniosoftware/invenio-records,tiborsimko/invenio-search