but most of it is empty, so use a map instead

Change-Id: I92fe46939e5107926fd4b92167bbace63f0376d5
Reviewed-on: https://gerrit.libreoffice.org/48830Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>