It is possible for rid not to be in partition_dict or new_partition_dict,
as this method is called from a master notification (partition changed),
which might happen outside of any replication (so when both dicts are
empty).

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2209 71dcc9de-d417-0410-9af5-da40c76e7ee4