since...

commit 8780fa41
Date:   Tue Oct 30 12:23:36 2018 +0100

    svtools: fix lost replacement grpahic when updating it via OLE fails

EmbeddedObjectRef::UpdateReplacementOnDemand is called by a chart during
EmbeddedObjectRef::GetReplacement which resets mpImpl->pGraphic to null

Change-Id: Id473b807582164eeb1791a26f6e0005a240f5989
Reviewed-on: https://gerrit.libreoffice.org/67128Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
Tested-by: Jenkins