Hitting /api/task/result/<id> for failed task will result in server error

[tebeka]

I have a "div" task which divides two numbers. I invoked it with /api/task/apply-async/div with 1 and 0 parameters (which will cause an exception). The flower server had the following error (and returned 500):

[E 121016 09:14:18 web:1085] Uncaught exception GET /api/task/result/cca8490d-db6f-4623-ab66-ec5cae53c29a (127.0.0.1)
    HTTPRequest(protocol='http', host='localhost:5555', method='GET', uri='/api/task/result/cca8490d-db6f-4623-ab66-ec5cae53c29a', version='HTTP/1.1', remote_ip='127.0.0.1', body='', headers={'Host': 'localhost:5555', 'Accept-Encoding': 'identity, deflate, compress, gzip', 'Accept': '*/*', 'User-Agent': 'python-requests/0.13.3 CPython/2.7.3 Linux/3.2.0-32-generic'})
    Traceback (most recent call last):
      File "/usr/local/lib/python2.7/dist-packages/tornado/web.py", line 1042, in _execute
        getattr(self, self.request.method.lower())(*args, **kwargs)
      File "/usr/local/lib/python2.7/dist-packages/tornado/web.py", line 1809, in wrapper
        return method(self, *args, **kwargs)
      File "/usr/local/lib/python2.7/dist-packages/flower/api/tasks.py", line 60, in get
        self.write(response)
      File "/usr/local/lib/python2.7/dist-packages/tornado/web.py", line 493, in write
        chunk = escape.json_encode(chunk)
      File "/usr/local/lib/python2.7/dist-packages/tornado/escape.py", line 90, in json_encode
        return _json_encode(recursive_unicode(value)).replace("</", "<\\/")
      File "/usr/lib/python2.7/json/__init__.py", line 231, in dumps
        return _default_encoder.encode(obj)
      File "/usr/lib/python2.7/json/encoder.py", line 201, in encode
        chunks = self.iterencode(o, _one_shot=True)
      File "/usr/lib/python2.7/json/encoder.py", line 264, in iterencode
        return _iterencode(o, 0)
      File "/usr/lib/python2.7/json/encoder.py", line 178, in default
        raise TypeError(repr(o) + " is not JSON serializable")
    TypeError: ZeroDivisionError('integer division or modulo by zero',) is not JSON serializable

[mher]

Thanks fixed!