fdo#81445: Display correct label for empty cell.

Change-Id: I4f3e99b2231f7cd87daa27ef2dc47d3bf37cea57
(cherry picked from commit 2202bda95c76127dffcc9c7460e462a877344b9c)
Reviewed-on: https://gerrit.libreoffice.org/10360
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>