Fix for fdo#80450: MS excel F functions help pages

F.DIST, F.DIST.RT, F.INV, F.INV.RT and F.TEST

Change-Id: Ia5cc2984c118f2d85872c80cd2ec6c533c94ff95
Reviewed-on: https://gerrit.libreoffice.org/10424
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>