Fix bug in rsync's delete_missing

[GabrielBianconi]

The code crashes if there are no files to delete when delete_missing=True.

---

IndexError                                Traceback (most recent call last)
Cell In[7], line 2
      1 s3_path = "s3://tensorzero-etl-online/data/organization_id=af98d0df-163b-4024-a7fd-7405c86215a0/workflow_id=98ecbc65-e853-4974-86e8-e9a7a9ba07d9/inference/function_id=0e1dc437-3bbe-49ee-9a63-36254a274c08/"
----> 2 read_from_s3_with_caching(s3_path)

Cell In[5], line 13
     10 print(dest)
     12 print(f"rsync...\n\t{source}\n\t->\n\t{dest})")
---> 13 fsspec.generic.rsync(s3_path, dest, delete_missing=True)
     15 print("Loading Parquet files...")
     17 parquet_paths = glob.glob(
     18     "**/*.parquet", root_dir=dest, recursive=True
     19 )

File /usr/local/lib/python3.10/dist-packages/fsspec/generic.py:139, in rsync(source, destination, delete_missing, source_field, dest_field, update_cond, inst_kwargs, fs, **kwargs)
    137 logger.debug(f"{len(to_delete)} files to delete")
    138 if delete_missing:
--> 139     fs.rm(to_delete)

File /usr/local/lib/python3.10/dist-packages/fsspec/asyn.py:118, in sync_wrapper.<locals>.wrapper(*args, **kwargs)
    115 @functools.wraps(func)
    116 def wrapper(*args, **kwargs):
    117     self = obj or args[0]
--> 118     return sync(self.loop, func, *args, **kwargs)

File /usr/local/lib/python3.10/dist-packages/fsspec/asyn.py:103, in sync(loop, func, timeout, *args, **kwargs)
    101     raise FSTimeoutError from return_result
    102 elif isinstance(return_result, BaseException):
--> 103     raise return_result
    104 else:
    105     return return_result

File /usr/local/lib/python3.10/dist-packages/fsspec/asyn.py:56, in _runner(event, coro, result, timeout)
     54     coro = asyncio.wait_for(coro, timeout=timeout)
     55 try:
---> 56     result[0] = await coro
     57 except Exception as ex:
     58     result[0] = ex

File /usr/local/lib/python3.10/dist-packages/fsspec/generic.py:256, in GenericFileSystem._rm(self, url, **kwargs)
    254 if isinstance(urls, str):
    255     urls = [urls]
--> 256 fs = _resolve_fs(urls[0], self.method)
    257 if fs.async_impl:
    258     await fs._rm(urls, **kwargs)

IndexError: list index out of range