Crash when using multiprocessing (`num_proc` > 1) on `filter` and all samples are discarded
## Describe the bug
If `filter` is applied to a dataset using multiprocessing (`num_proc` > 1) and all sharded datasets are empty afterwards (due to all samples being discarded), the program crashes.

## Steps to reproduce the bug
```python
from datasets import Dataset
data = Dataset.from_dict({'id': [0,1]})
data.filter(lambda x: False, num_proc=2)
```

## Expected results
An empty table should be returned without crashing.

## Actual results
```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/user/venv/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 185, in wrapper
    out: Union["Dataset", "DatasetDict"] = func(self, *args, **kwargs)
  File "/home/user/venv/lib/python3.8/site-packages/datasets/fingerprint.py", line 397, in wrapper
    out = func(self, *args, **kwargs)
  File "/home/user/venv/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 2143, in filter
    return self.map(
  File "/home/user/venv/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 1738, in map
    result = concatenate_datasets(transformed_shards)
  File "/home/user/venv/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 3267, in concatenate_datasets
    table = concat_tables(tables_to_concat, axis=axis)
  File "/home/user/venv/lib/python3.8/site-packages/datasets/table.py", line 853, in concat_tables
    return ConcatenationTable.from_tables(tables, axis=axis)
  File "/home/user/venv/lib/python3.8/site-packages/datasets/table.py", line 713, in from_tables
    blocks = to_blocks(tables[0])
IndexError: list index out of range
```

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 1.9.0
- Platform: Linux-5.12.11-300.fc34.x86_64-x86_64-with-glibc2.2.5
- Python version: 3.8.10
- PyArrow version: 3.0.0
