PT: clear shuffler buffers in reset()

Author: NeoLegends

returnn/torch/data/pipeline.py

@@ -547,6 +547,8 @@ def set_seed(self, seed: int) -> ShufflingDataPipe:
 
     def reset(self):
         """resets the internal state of the data pipe"""
+        self._buffer.clear()
+        self._next_buffer.clear()
         if self._seed is None:
             self._seed = int(torch.empty((), dtype=torch.int32).random_().item())
         self._rng.seed(self._seed)