fix copying of maVectorGraphicData in ImpGraphic

a8c9f2f6 removed copying of
maVectorGraphicData by mistake in operator= which means that the
source of SVG files won't be copied and will disappear.

Change-Id: I339b65e6b54215d6a108a00d630916e94da24e21
Reviewed-on: https://gerrit.libreoffice.org/72097Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>

vcl/source/gdi/impgraph.cxx

@@ -260,6 +260,7 @@ ImpGraphic& ImpGraphic::operator=( const ImpGraphic& rImpGraphic )
             }
         }
 
+        maVectorGraphicData = rImpGraphic.maVectorGraphicData;
         mpPdfData = rImpGraphic.mpPdfData;
     }