Client: Fix opaque region setter
The rect is in the global coordinate system, while the opaque region must be in the surface local coordinate system.
Change-Id: I75042b4d779dfd4dfe610aad1f0387879f11b048 Reviewed-by: Aleix Pol Gonzalez aleixpol@kde.org (cherry picked from commit f9425f57)
It's needed to fix overdraw in kwin because some Qt clients, e.g. plasmashell, don't set correct opaque region