+packagebugs-search crashes when field.sourcepackagename is a non-existent package

[Diogo Matsubara]

    affects /products/malone
    status confirmed

Steps to reproduce (using sample data):
1. Open http://launchpad.dev/people/ubuntu-team/+packagebugs-search?field.distribution=ubuntu&field.sourcepackagename=foo
2. Crash like: OOPS-299A2

field.sourcepackagename must be a existent sourcepackagename. This bug happens
when you change the URL manually; It should raise an UnexpectedFormData.

This URL will recreate the issue on staging:
https://staging.launchpad.net/~xubuntu-team/+packagebugs-search?field.distribution=ubuntu&field.sourcepackagename=fooblah

Module lp.registry.browser.person, line 1934, in current_package
self.widgets['sourcepackagename'].getInputValue()):
Module zope.app.form.browser.widget, line 321, in getInputValue
raise self._error
ConversionError: ('Invalid value', InvalidValue("token u'fooblah' not found in vocabulary"))

The page is already being rendered at this point.

[Launchpad QA Bot (lpqabot)]

Fixed in stable r12384 <http://bazaar.launchpad.net/~launchpad-pqm/launchpad/stable/revision/12384>.