to reduce needless object creation and copying some more

And fix what looks like a bug in CSS hex color parsing at line
609 in sw/../parcss1.cxx that has been there since
commit 7b0b5cdf "initial import"

Change-Id: Ibad42b23721a56493bd1edcd7165e6104494a5c3
Reviewed-on: https://gerrit.libreoffice.org/58357
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>