fix trainer when dataloader not using batch_sampler

deepspeech/training/trainer.py

@@ -181,7 +181,7 @@ class Trainer():
         """Reset the train loader seed and increment `epoch`.
         """
         self.epoch += 1
-        if self.parallel:
+        if self.parallel and hasattr(self.train_loader, "batch_sampler"):
             self.train_loader.batch_sampler.set_epoch(self.epoch)
 
     def train(self):
@@ -191,7 +191,7 @@ class Trainer():
             # save init model, i.e. 0 epoch
             self.save(tag='init', infos=None)
         self.lr_scheduler.step(self.epoch)
-        if self.parallel:
+        if self.parallel and hasattr(self.train_loader, "batch_sampler"):
             self.train_loader.batch_sampler.set_epoch(self.epoch)
 
         logger.info(f"Train Total Examples: {len(self.train_loader.dataset)}")