[click] allow downloads for published gratis apps without the user having to sign in to sca

[James Westby]

  AttributeError: 'NoneType' object has no attribute 'has_perm'

      File "/srv/sc.ubuntu.com/production/software-center-agent/sourcecode/django/django/core/handlers/base.py", line 115, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/srv/sc.ubuntu.com/production/software-center-agent/sourcecode/django/django/views/decorators/cache.py", line 89, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "/srv/sc.ubuntu.com/production/software-center-agent/sourcecode/django/django/views/decorators/vary.py", line 19, in inner_func
    response = func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston/resource.py", line 166, in __call__
    result = self.error_handler(e, request, meth, em_format)
  File "/usr/lib/python2.7/dist-packages/piston/resource.py", line 164, in __call__
    result = meth(request, *args, **kwargs)
  File "/srv/sc.ubuntu.com/production/software-center-agent/src/softwarecenteragent/api/handlers.py", line 267, in read
    is_reviewer = can_review(user, package)
  File "/srv/sc.ubuntu.com/production/software-center-agent/src/devportal/views.py", line 154, in can_review
    return user.has_perm('devportal.review_application')

This occurs if the user hasn't ever signed in to sca. We can still allow them to download published
gratis apps, but not anything that requires a user record (unpublished or paid).