WebSession: bug fix for isUserGuest()
WebSession: bug fix for isUserGuest()

* Fixes bug in isUserGuest() that was introduced in
  f0f34d2c1bfd29ef3f11621f8e4251065da27e66.

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