Currently, negative scaling (mirroring) is lost in
SdrTextObj::NbcSetSnapRect, when rect is justified.
This patch cares for this.

Possibly it's better to make these changes directly in
SdrTextObj::NbcSetSnapRect?

Change-Id: I353ff01626e15b398de95e28eae78572991dfdc3
Reviewed-on: https://gerrit.libreoffice.org/20109Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Armin Le Grand <Armin.Le.Grand@cib.de>