URL hacking to +initseries for an already-initialized series OOPSes

Traceback (most recent call last):

Module zope.publisher.publish, line 134, in publish
result = publication.callObject(request, obj)
Module canonical.launchpad.webapp.publication, line 498, in callObject
return mapply(ob, request.getPositionalArguments(), request)
Module zope.publisher.publish, line 109, in mapply
return debug_call(obj, args)
__traceback_info__: <security proxied zope.browserpage.metaconfigure.SimpleViewClass from /srv/launchpad.net/codelines/trunk/lib/lp/registry/browser/../templates/distroseries-initialize.pt instance at 0xca3e68c>
Module zope.publisher.publish, line 115, in debug_call
return obj(*args)
Module canonical.launchpad.webapp.publisher, line 303, in __call__
self.initialize()
Module lp.registry.browser.distroseries, line 671, in initialize
self.context.previous_series)
Module lp.registry.browser.distroseries, line 645, in seriesToVocab
'value': series.id,
AttributeError: 'NoneType' object has no attribute 'id'<br />

In this case previous_series is None, which is correct for the first series in a new distro.

We can do one of 2 things:
1. redirect +initseries back to the series page
2. make it work properly and say that the series is already initialized