Fails to handle empty intermediate responses from miser mode

[danmichaelo]

When using the gcmnamespace filter with generator=categorymembers, there is a note in the ApiSandbox:

Note: Due to miser mode, using this may result in fewer than cmlimit results returned before continuing; in extreme cases, zero results may be returned.

Turns out the zero result responses do not include the 'query' key at all:

~/projects/wp/mwclient/mwclient/listing.py in set_iter(self, data)
    109     def set_iter(self, data):
    110         """Set `self._iter` to the API response `data`."""
--> 111         if self.result_member not in data['query']:
    112             self._iter = iter(six.moves.range(0))
    113         elif type(data['query'][self.result_member]) is list:

KeyError: 'query'