fix dataloader not restart

ppdet/data/reader.py

@@ -136,7 +136,7 @@ class BaseDataLoader(object):
         else:
             self._batch_sampler = batch_sampler
 
-        self.loader = DataLoader(
+        self.dataloader = DataLoader(
             dataset=self.dataset,
             batch_sampler=self._batch_sampler,
             collate_fn=self._batch_transforms,
@@ -145,7 +145,7 @@ class BaseDataLoader(object):
             return_list=return_list,
             use_buffer_reader=use_prefetch,
             use_shared_memory=False)
-        self.loader = iter(self.loader)
+        self.loader = iter(self.dataloader)
 
         return self
 
@@ -163,6 +163,7 @@ class BaseDataLoader(object):
             data = next(self.loader)
             return {k: v for k, v in zip(self._fields, data)}
         except StopIteration:
+            self.loader = iter(self.dataloader)
             six.reraise(*sys.exc_info())
 
     def next(self):