Dataset Viewer issue for timit_asr
Yes, the dataset viewer is based on `datasets`, and the following does not work:

```
>>> from datasets import get_dataset_split_names
>>> get_dataset_split_names('timit_asr')
Downloading builder script: 7.48kB [00:00, 6.69MB/s]
Traceback (most recent call last):
  File "/home/slesage/hf/datasets-server/services/worker/.venv/lib/python3.9/site-packages/datasets/inspect.py", line 354, in get_dataset_config_info
    for split_generator in builder._split_generators(
  File "/home/slesage/.cache/huggingface/modules/datasets_modules/datasets/timit_asr/43f9448dd5db58e95ee48a277f466481b151f112ea53e27f8173784da9254fb2/timit_asr.py", line 117, in _split_generators
    data_dir = os.path.abspath(os.path.expanduser(dl_manager.manual_dir))
  File "/home/slesage/.pyenv/versions/3.9.6/lib/python3.9/posixpath.py", line 231, in expanduser
    path = os.fspath(path)
TypeError: expected str, bytes or os.PathLike object, not NoneType

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/slesage/hf/datasets-server/services/worker/.venv/lib/python3.9/site-packages/datasets/inspect.py", line 404, in get_dataset_split_names
    info = get_dataset_config_info(
  File "/home/slesage/hf/datasets-server/services/worker/.venv/lib/python3.9/site-packages/datasets/inspect.py", line 359, in get_dataset_config_info
    raise SplitsNotFoundError("The split names could not be parsed from the dataset config.") from err
datasets.inspect.SplitsNotFoundError: The split names could not be parsed from the dataset config.
```

cc @huggingface/datasets  Due to license restriction, this dataset needs manual downloading of the original data.

This information is in the dataset card: https://huggingface.co/datasets/timit_asr
> The dataset needs to be downloaded manually from https://catalog.ldc.upenn.edu/LDC93S1 Maybe a better error message for datasets that need manual downloading? @severo 

Maybe we can raise a specific excpetion as done from `load_dataset`... Yes, ideally something like https://github.com/huggingface/datasets/blob/main/src/datasets/builder.py#L81
 The preview is now disabled (and a descriptive warning is displayed) for datasets requiring manual download. See:

![timit_asr-manual-download](https://user-images.githubusercontent.com/8515462/193578572-3d21b790-f848-4257-9e9b-7cab3d76a269.png)

### Link

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### Description

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### Owner

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