prevent packages update in organization_update

I'm getting a NotFound error from package_show when I call organization_update from the API.

```
  File "/home/ian/git/ckan/ckan/logic/__init__.py", line 329, in wrapped
    return _action(context, data_dict, **kw)
  File "/home/ian/git/ckan/ckan/logic/action/update.py", line 567, in organization_update
    return _group_or_org_update(context, data_dict, is_org=True)
  File "/home/ian/git/ckan/ckan/logic/action/update.py", line 463, in _group_or_org_update
    group = model_save.group_dict_save(data, context)
  File "/home/ian/git/ckan/ckan/lib/dictization/model_save.py", line 446, in group_dict_save
    map( rebuild, package_ids )
  File "/home/ian/git/ckan/ckan/lib/search/__init__.py", line 156, in rebuild
    {'id': package_id})
  File "/home/ian/git/ckan/ckan/logic/__init__.py", line 329, in wrapped
    return _action(context, data_dict, **kw)
  File "/home/ian/git/ckan/ckan/logic/action/get.py", line 748, in package_show
    raise NotFound
```