Do not fail if _base_metadata does not exists

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@28081 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5OOo/Document/OOoDocument.py

@@ -546,7 +546,7 @@ class OOoDocument(PermanentURLMixIn, File, ConversionCacheMixin):
       Returns the metadata extracted by the conversion
       server.
     """
-    return self._base_metadata
+    return getattr(self, '_base_metadata', {})
 
   security.declareProtected(Permissions.ModifyPortalContent,
                             'updateBaseMetadata')