Fix input data file extension in examples (#28741)

examples/pytorch/summarization/run_summarization_no_trainer.py

@@ -404,9 +404,10 @@ def main():
         data_files = {}
         if args.train_file is not None:
             data_files["train"] = args.train_file
+            extension = args.train_file.split(".")[-1]
         if args.validation_file is not None:
             data_files["validation"] = args.validation_file
-        extension = args.train_file.split(".")[-1]
+            extension = args.validation_file.split(".")[-1]
         raw_datasets = load_dataset(extension, data_files=data_files)
     # See more about loading any type of standard or custom dataset (from files, python dict, pandas DataFrame, etc) at
     # https://huggingface.co/docs/datasets/loading_datasets.