coverity#735766 Unchecked dynamic_cast

Change-Id: I7f69e2a9d83d4632a23c6b1b15156b8e084487e2

oox/source/shape/ShapeContextHandler.cxx

@@ -420,6 +420,8 @@ ShapeContextHandler::getShape() throw (uno::RuntimeException, std::exception)
                 for (std::vector<OUString>::const_iterator aIt = mpShape->getExtDrawings().begin(); aIt != mpShape->getExtDrawings().end(); ++aIt)
                 {
                     DiagramGraphicDataContext* pDiagramGraphicDataContext = dynamic_cast<DiagramGraphicDataContext*>(mxDiagramShapeContext.get());
+                    if (!pDiagramGraphicDataContext)
+                        break;
                     OUString aFragmentPath(pDiagramGraphicDataContext->getFragmentPathFromRelId(*aIt));
                     oox::drawingml::ShapePtr pShapePtr( new Shape( "com.sun.star.drawing.GroupShape" ) );
                     pShapePtr->setDiagramType();