More vertical space for the options dialog

The vertical space of the options dialog is to small for the new
security page in German translation. The last entry is not visible
and the button could not be reached.
Solution: I added more vertical space to ROW_3 which is the postion
of the separation line. I added the hight of a button and of the line.
This fixes the issue with missing space for the last entry in section
especially for the German translation.

Change-Id: Icacfd4587d605e56438f3d7207ce5d257f313072
Reviewed-on: https://gerrit.libreoffice.org/8735
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>