Fix pad_token_tensor is None in warning (huggingface#34005)

Fix pad_token_tensor is None in warning

src/transformers/generation/utils.py

@@ -1866,8 +1866,8 @@ def _tensor_or_none(token, device=None):
                         "The attention mask and the pad token id were not set. As a consequence, you may observe "
                         "unexpected behavior. Please pass your input's `attention_mask` to obtain reliable results."
                     )
-                logger.warning(f"Setting `pad_token_id` to `eos_token_id`:{pad_token_tensor} for open-end generation.")
             pad_token_tensor = eos_token_tensor[0]
+            logger.warning(f"Setting `pad_token_id` to `eos_token_id`:{pad_token_tensor} for open-end generation.")
 
         # Sanity checks/warnings
         if self.config.is_encoder_decoder and decoder_start_token_tensor is None: