fix webdataset filename split
MEMBER
Hi ! This was fixed recently in https://github.com/huggingface/datasets/pull/6904 and https://github.com/huggingface/datasets/pull/6931
2024-06-04T12:54:04Z
https://github.com/huggingface/datasets/pull/6849#issuecomment-2147464556
https://api.github.com/repos/huggingface/datasets/issues/6849
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2024-06-04T12:54:04Z
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use `os.path.splitext` to parse field_name.

fix filename which has dot. like:

```
a.b.jpeg
a.b.txt
```