Safeguarding DL2Iterator's __getattr__ (#1004)

Summary:
Pull Request resolved: #1004

Fixes #1000

As reported in the issue, in some uncommon cases, it is possible for the attribute to be missing, leading to infinite recursion. This should prevent it.

Test Plan: Imported from OSS

Reviewed By: ejguan

Differential Revision: D43197744

Pulled By: NivekT

fbshipit-source-id: 64e6edfe129dcca06f5cf3054bb7f8c2e510536c

Author: NivekT

torchdata/dataloader2/dataloader2.py

@@ -77,7 +77,7 @@ def __getattr__(self, name):
         """
         To delegate operations to ``dataloader._datapipe_iter``.
         """
-        if self.dataloader._datapipe_iter is None:
+        if "dataloader" not in self.__dict__ or self.dataloader._datapipe_iter is None:
             raise AttributeError
         return getattr(self.dataloader._datapipe_iter, name)