TypeError when trying to copy parquet files
On https://huggingface.co/datasets/bigcode/the-stack, we get:

```json
{
  "error": "unsupported operand type(s) for +=: 'NoneType' and 'int'",
  "cause_exception": "TypeError",
  "cause_message": "unsupported operand type(s) for +=: 'NoneType' and 'int'",
  "cause_traceback": [
    "Traceback (most recent call last):\n",
    " File \"/src/services/worker/src/worker/job_manager.py\", line 163, in process\n job_result = self.job_runner.compute()\n",
    " File \"/src/services/worker/src/worker/job_runners/config/parquet_and_info.py\", line 931, in compute\n compute_config_parquet_and_info_response(\n",
    " File \"/src/services/worker/src/worker/job_runners/config/parquet_and_info.py\", line 818, in compute_config_parquet_and_info_response\n fill_builder_info(builder, hf_token=hf_token)\n",
    " File \"/src/services/worker/src/worker/job_runners/config/parquet_and_info.py\", line 650, in fill_builder_info\n builder.info.download_size += sum(sizes)\n",
    "TypeError: unsupported operand type(s) for +=: 'NoneType' and 'int'\n"
  ]
}
```

Error is here: https://github.com/huggingface/datasets-server/blob/e0eed9c9ad09d57a857e6498c44b76d6bd71ff76/services/worker/src/worker/job_runners/config/parquet_and_info.py#L650
TypeError when trying to copy parquet files: On https://huggingface.co/datasets/bigcode/the-stack, we get:

```json
{
  "error": "unsupported operand type(s) for +=: 'NoneType' and 'int'",
  "cause_exception": "TypeError",
  "cause_message": "unsupported operand type(s) for +=: 'NoneType' and 'int'",
  "cause_traceback": [
    "Traceback (most recent call last):\n",
    " File \"/src/services/worker/src/worker/job_manager.py\", line 163, in process\n job_result = self.job_runner.compute()\n",
    " File \"/src/services/worker/src/worker/job_runners/config/parquet_and_info.py\", line 931, in compute\n compute_config_parquet_and_info_response(\n",
    " File \"/src/services/worker/src/worker/job_runners/config/parquet_and_info.py\", line 818, in compute_config_parquet_and_info_response\n fill_builder_info(builder, hf_token=hf_token)\n",
    " File \"/src/services/worker/src/worker/job_runners/config/parquet_and_info.py\", line 650, in fill_builder_info\n builder.info.download_size += sum(sizes)\n",
    "TypeError: unsupported operand type(s) for +=: 'NoneType' and 'int'\n"
  ]
}
```

Error is here: https://github.com/huggingface/datasets-server/blob/e0eed9c9ad09d57a857e6498c44b76d6bd71ff76/services/worker/src/worker/job_runners/config/parquet_and_info.py#L650