fdo#37401 - fixed the old vector length

The center-left point in the area is used to calculate the old vector length but the coordinate was incorrect.

Change-Id: I81a88182d11e30ee7a5caee3eac879b082bff160
Reviewed-on: https://gerrit.libreoffice.org/9887
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>