New functionality added to pivot table became fully
broken with Eike's revertion:
50244309
This commit fixes this problem.

Change-Id: I67cfc63305bb9b2edeed2abd26d729fbf650579f
Reviewed-on: https://gerrit.libreoffice.org/31096Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>
Tested-by: Tamás Zolnai <tamas.zolnai@collabora.com>