get_ip() fails if any meta field from IPWARE_META_PRECEDENCE_LIST is None

[HageMaster3108]

Hi there,

if any of the META keys in IPWARE_META_PRECEDENCE_LIST happens to be undefined/None, get_ip() fails.

Traceback:
File "/Users/patrick/.virtualenvs/ib-cms/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/Users/patrick/.virtualenvs/ib-cms/lib/python2.7/site-packages/django/views/decorators/csrf.py" in wrapped_view
  58.         return view_func(*args, **kwargs)
File "/Users/patrick/Dev/ib-main/cms/views.py" in fallback_upload_view
  192.                 queue.client_ip = get_ip(request)
File "/Users/patrick/.virtualenvs/ib-cms/lib/python2.7/site-packages/ipware/ip.py" in get_ip
  14.         value = request.META.get(key, '').strip()

Will send a pull request...