Fix FDO#80441 Help pages for WEBSERVICES function

Also FILTERXML.
Many thanks to Leif Lodahl for the help

Change-Id: I241610db69eab0cc2490492520288bc6b154c21b
Reviewed-on: https://gerrit.libreoffice.org/11435
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>