bad URLs cause 500 errors where 404s would be expected

[Curtis Hovey]

My URL hack to verify errors are logged app.log as well as emailed illustrates a weakness in the code:

2013-04-29 18:13:55,183 http://staging.jujucharms.com/api/0/charms/interesting/bing
Traceback (most recent call last):
  File "/home/webops_deploy/charmworld/local/lib/python2.7/site-packages/pyramid_exclog/__init__.py", line 44, in exclog_tween
    return handler(request)
  File "/home/webops_deploy/charmworld/local/lib/python2.7/site-packages/pyramid/router.py", line 161, in handle_request
    response = view_callable(context, request)
  File "/home/webops_deploy/charmworld/local/lib/python2.7/site-packages/pyramid/config/views.py", line 375, in viewresult_to_response
    result = view(context, request)
  File "/home/webops_deploy/charmworld/local/lib/python2.7/site-packages/pyramid/config/views.py", line 465, in _class_requestonly_view
    response = inst()
  File "/home/webops_deploy/charmworld/charmworld/views/api.py", line 91, in __call__
    result = self._handle(handler, args, kwargs)
  File "/home/webops_deploy/charmworld/charmworld/views/api.py", line 64, in _handle
    return handler(*args, **kwargs)
  File "/home/webops_deploy/charmworld/charmworld/views/api.py", line 292, in charms
    return self._handle(handler, args, kwargs)
UnboundLocalError: local variable 'handler' referenced before assignment

API0.charms() assumes it will always find a handler for the URL. I expect a 404 to be returned when I URL hack.