None check before getattr

if social isn't initialized properly, you will get this:

....
  File "/Users/baran/Developer/argume/venv/lib/python2.7/site-packages/flask_social/core.py", line 146, in __getattr__
    return getattr(self._state, name, None)
  File "/Users/baran/Developer/argume/venv/lib/python2.7/site-packages/flask_social/core.py", line 146, in __getattr__
    return getattr(self._state, name, None)
  File "/Users/baran/Developer/argume/venv/lib/python2.7/site-packages/flask_social/core.py", line 146, in __getattr__
    return getattr(self._state, name, None)
  File "/Users/baran/Developer/argume/venv/lib/python2.7/site-packages/flask_social/core.py", line 146, in __getattr__
    return getattr(self._state, name, None)
RuntimeError: maximum recursion depth exceeded while calling a Python object