stat has no st_flags on Windows (maybe elsewhere?)

IPython/html/base/handlers.py

@@ -305,7 +305,8 b' class AuthenticatedFileHandler(IPythonHandler, web.StaticFileHandler):'
         # check UF_HIDDEN on any location up to root
         path = absolute_path
         while path and path.startswith(absolute_root):
-            if os.stat(path).st_flags & UF_HIDDEN:
+            st = os.stat(path)
+            if getattr(st, 'st_flags', 0) & UF_HIDDEN:
                 raise web.HTTPError(403)
             path, _ = os.path.split(path)