bnc#812796: Don't create data series when the series has no values.

Change-Id: I92e2d7a3fab0948aea0557cf3cb65d57d48f3f59
(cherry picked from commit 5e2b7e37a29edf45f829ccee2302a942b54568a1)
Reviewed-on: https://gerrit.libreoffice.org/10039
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>