fdo#76032: This row index is 1-based whereas our own mnRow is 0-based.

Change-Id: I098d300532bef164bef0d40ebf62a6848bc19cb8
(cherry picked from commit ff56553e34dfed01b9226ce7a516dbeb6da32124)
Reviewed-on: https://gerrit.libreoffice.org/8577
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>