The consequence was that the shapes were inserted into the background
layer.

The problem was particularly visible with the LOK, but reproducible on
the desktop too.

Includes unit test.

Change-Id: I16137331f944101e25679ec8c4a034bea658bc57
Reviewed-on: https://gerrit.libreoffice.org/66917
Tested-by: Jenkins
Reviewed-by: Jan Holesovsky <kendy@collabora.com>