头像上传出错会直接返回 Traceback 信息

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/tornado/web.py", line 1332, in _execute
    result = method(*self.path_args, **self.path_kwargs)
  File "/usr/local/lib/python2.7/dist-packages/tornado/web.py", line 2607, in wrapper
    return method(self, *args, **kwargs)
  File "/data/www/v2ex/galaxy/handlers/web/settings.py", line 535, in post
    avatar73 = self.rescale(avatar, 73, 73)
  File "/data/www/v2ex/galaxy/handlers/__init__.py", line 745, in rescale
    img = pil.open(input_file)
  File "/usr/local/lib/python2.7/dist-packages/PIL/Image.py", line 2288, in open
    % (filename if filename else fp))
IOError: cannot identify image file <cStringIO.StringI object at 0x7f04f64179c0>