Fix fdo#80656. Help for NUMBERVALUE Calc function

Change-Id: Iab3c6e2a82162f5b6cbd1a2e80e76e7df36b2042
Reviewed-on: https://gerrit.libreoffice.org/9959
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>