Raise a proper exception when trying to stream a dataset that requires to manually download files
MEMBER
Hi @severo, thanks for reporting.

As discussed, datasets requiring manual download should be:
- programmatically identifiable
- properly handled with more clear error message when trying to load them with streaming

In relation with programmatically identifiability, note that for datasets requiring manual download, their builder have a property `manual_download_instructions` which is not None:
```python
# Dataset requiring manual download:
builder.manual_download_instructions is not None
```
2021-08-04T07:26:11Z
https://github.com/huggingface/datasets/issues/2749#issuecomment-892430477
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COLLABORATOR
Thanks @albertvillanova 
2021-08-09T08:53:35Z
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## Describe the bug

At least for 'reclor', 'telugu_books', 'turkish_movie_sentiment', 'ubuntu_dialogs_corpus', 'wikihow', trying to `load_dataset` in streaming mode raises a `TypeError` without any detail about why it fails.

## Steps to reproduce the bug

```python
from datasets import load_dataset
dataset = load_dataset("reclor", streaming=True)
```

## Expected results

Ideally: raise a specific exception, something like `ManualDownloadError`.

Or at least give the reason in the message, as when we load in normal mode:

```python
from datasets import load_dataset
dataset = load_dataset("reclor")
```

```
AssertionError: The dataset reclor with config default requires manual data.
 Please follow the manual download instructions:   to use ReClor you need to download it manually. Please go to its homepage (http://whyu.me/reclor/) fill the google
  form and you will receive a download link and a password to extract it.Please extract all files in one folder and use the path folder in datasets.load_dataset('reclor', data_dir='path/to/folder/folder_name')
  .
 Manual data can be loaded with `datasets.load_dataset(reclor, data_dir='<path/to/manual/data>')
```

## Actual results

```
TypeError: expected str, bytes or os.PathLike object, not NoneType
```

## Environment info

- `datasets` version: 1.11.0
- Platform: macOS-11.5-x86_64-i386-64bit
- Python version: 3.8.11
- PyArrow version: 4.0.1
