[ccplugin] do not crash if an entity failed to serialize

otherwise the import just hand forever.

cubicweb_elasticsearch/ccplugin.py

@@ -102,8 +102,14 @@
             cnx.debug(u'RQL: {}'.format(rql))
 
             for entity in rset.entities():
-                serializer = entity.cw_adapt_to('IFullTextIndexSerializable')
-                json = serializer.serialize()
+                try:
+                    serializer = entity.cw_adapt_to('IFullTextIndexSerializable')
+                    json = serializer.serialize()
+                except Exception as e:
+                    cnx.error('[{}] Failed to serialize entity {} ({})'.format(
+                        index_name, entity.eid, etype))
+                    continue
+
                 if not dry_run and json:
                     # Entities with
                     # fulltext_containers relations return their container