Its sole client code in sw/source/uibase/docvw/edtwin.cxx allows the
precondition that its 2nd argument rWords is empty.

This also corrects the @param description of the argument.

Change-Id: Icc12bc36d0d4157ed05ef10fb3c3db325c6bfaf2
Reviewed-on: https://gerrit.libreoffice.org/55943
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>