get value by reference

introduced in
commit 8c2f2e1d and
commit f9b200ce

Change-Id: Iba84dd752f4cbdde9f3676c434d107efabe63a38
Reviewed-on: https://gerrit.libreoffice.org/23974Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>