BibMerge: fix record selection bug
BibMerge: fix record selection bug

* Fixes syntax error related to the selection option change introduced in
  c4445c5896324f68e495b2f6fa245e30888e7d7f that was preventing BibMerge
  interface's record selection box from working.

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