Handle NotADirectoryError in include_exists()

A recent commit removed this favor of `IsADirectoryError`. In fact both
exceptions need to be handled.

_shared/local_extensions.py

@@ -150,7 +150,7 @@ def include_exists(self, context, path):
         try:
             with self._open(context, path):
                 return True
-        except (FileNotFoundError, IsADirectoryError):
+        except (FileNotFoundError, IsADirectoryError, NotADirectoryError):
             return False
 
     @pass_context