WebStyle: fix bug in pageheader template
WebStyle: fix bug in pageheader template

* Fixes a small issue which would case an exception when rendering
  certain pages.

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

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