Only sort if had a chance to add something

Change-Id: I54ec1368ab64d422de13217e877076a3ee41de94
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/177456
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Jenkins

sc/source/filter/xml/xmlexprt.cxx

@@ -696,8 +696,8 @@ void ScXMLExport::GetAreaLinks( ScMyAreaLinksContainer& rAreaLinks )
                 rAreaLinks.AddNewAreaLink( aAreaLink );
             }
         }
+        rAreaLinks.Sort();
     }
-    rAreaLinks.Sort();
 }
 
 // core implementation