if we're doing a find/insert on a set or a map, it is better to just do
a conditional insert/emplace operation than triggering two lookups.

Change-Id: I80da5097f5a89fe30fa348ce5b6e747c34287a8d
Reviewed-on: https://gerrit.libreoffice.org/70937
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>