Fix GCC 4.8 build of abstract3drenderer

Task-number: QTBUG-77730
Change-Id: I827d727b103a9923a8b82163bfa4f77c81c0906b
Reviewed-by: Liang Qi <liang.qi@qt.io>

src/datavisualization/engine/abstract3drenderer.cpp

@@ -234,7 +234,7 @@ void Abstract3DRenderer::initializeOpenGL()
     loadLabelMesh();
     loadPositionMapperMesh();
 
-    QObject::connect(m_context, &QOpenGLContext::aboutToBeDestroyed,
+    QObject::connect(m_context.data(), &QOpenGLContext::aboutToBeDestroyed,
                      this, &Abstract3DRenderer::contextCleanup);
 }