fdo#72967 Draw position size tab - min size is 0 not 1 (mm)

Adjustment for size of an object had the minimum set to 1 (mm)
instead of 0.

Change-Id: I7d4c0998d2987448cea0fd7934649c02a513ac06
Reviewed-on: https://gerrit.libreoffice.org/8072
Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>