set Referer on link mediadescriptor

to allow determining if the source document is from a trusted/untrusted
location

Change-Id: I780568652d2ef0cc8543c27ba26289277b5d9d0c
Reviewed-on: https://gerrit.libreoffice.org/53689Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sw/source/filter/xml/xmltexti.cxx

@@ -572,16 +572,21 @@ uno::Reference< XPropertySet > SwXMLTextImportHelper::createAndInsertOOoLink(
         uno::Sequence< beans::PropertyValue > aMediaDescriptor( 1 );
         aMediaDescriptor[0].Name = "URL";
         aMediaDescriptor[0].Value <<= aURLObj.GetMainURL( INetURLObject::DecodeMechanism::NONE );
-        if ( pDoc->GetDocShell() && pDoc->GetDocShell()->GetMedium() )
+
+        if (SfxMedium* pMedium = pDoc->GetDocShell() ? pDoc->GetDocShell()->GetMedium() : nullptr)
         {
-            uno::Reference< task::XInteractionHandler > xInteraction =
-                                        pDoc->GetDocShell()->GetMedium()->GetInteractionHandler();
+            uno::Reference< task::XInteractionHandler > xInteraction = pMedium->GetInteractionHandler();
             if ( xInteraction.is() )
             {
                 aMediaDescriptor.realloc( 2 );
                 aMediaDescriptor[1].Name = "InteractionHandler";
                 aMediaDescriptor[1].Value <<= xInteraction;
             }
+
+            const auto nLen = aMediaDescriptor.getLength() + 1;
+            aMediaDescriptor.realloc(nLen);
+            aMediaDescriptor[nLen - 1].Name = "Referer";
+            aMediaDescriptor[nLen - 1].Value <<= pMedium->GetName();
         }
 
         uno::Reference < embed::XEmbeddedObject > xObj(