Fix decode error when using wsgi container and enter erroneous url.

You can know below url is erroneous utf-8 url.
 http://foo.bar/%EB%82%98%EC%99

If upper one inputted default server, it hasn't problem. But upper one inputted wsgi container, occur below error.

          File "/home/username/pyenv/local/lib/python2.7/site-packages/werkzeug/routing.py", line 1202, in bind_to_environ
            path_info = _get_wsgi_string('PATH_INFO')
          File "/home/username/pyenv/local/lib/python2.7/site-packages/werkzeug/routing.py", line 1199, in _get_wsgi_string
            return wsgi_decoding_dance(val, self.charset)
          File "/home/username/pyenv/local/lib/python2.7/site-packages/werkzeug/_compat.py", line 92, in wsgi_decoding_dance
            return s.decode(charset)
          File "/home/username/pyenv/lib/python2.7/encodings/utf_8.py", line 16, in decode
            return codecs.utf_8_decode(input, errors, True)
        UnicodeDecodeError: 'utf8' codec can't decode bytes in position 3-4: unexpected end of data

This pull request fixed that error.