pass originURL to the substitue graphic - work-around

We need to pretend that the substitue graphic has a originURL of
the original for now. Once Graphic will handle all the swapping
and substitution this won't be necessary anymore.

Change-Id: I9590b741c94d06d1b484273cc4ba5517951b77ec
Reviewed-on: https://gerrit.libreoffice.org/49647Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>

svtools/source/graphic/grfcache.cxx

@@ -305,7 +305,9 @@ void GraphicCacheEntry::AddGraphicObjectReference( const GraphicObject& rObj, Gr
     if( mbSwappedAll )
         mbSwappedAll = !ImplInit( rObj );
 
+    OUString rOriginURL = rObj.GetGraphic().getOriginURL();
     ImplFillSubstitute( rSubstitute );
+    rSubstitute.setOriginURL(rOriginURL);
     maGraphicObjectList.push_back( const_cast<GraphicObject*>(&rObj) );
 }