coverity#1421068 Uncaught exception

see if using copy ctor rather than default dtor keeps it happy

Change-Id: I539271a569fa769a4cb33f71b8bf871dee810abf
Reviewed-on: https://gerrit.libreoffice.org/45248Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

svtools/source/graphic/grfmgr.cxx

@@ -94,6 +94,7 @@ GraphicObject::GraphicObject(const Graphic& rGraphic)
 GraphicObject::GraphicObject(const GraphicObject& rGraphicObj)
     : maGraphic(rGraphicObj.GetGraphic())
     , maAttr(rGraphicObj.maAttr)
+    , maPrefMapMode(rGraphicObj.maPrefMapMode)
     , maLink(rGraphicObj.maLink)
     , maUserData(rGraphicObj.maUserData)
     , mbAutoSwapped(false)