Fix listing files in BucketFS for empty bucket (-location)

[ckunki]

For listing files in the BucketFS or one of its folders, BFS provides method PathLike.iterdir().

When creating a list of all the filenames, iterdir() will be called one or multiple times:

names = [f.name for f in bfs_location.iterdir()]

If the specified BucketFS location is empty, BFSPY raises a FileNotFoundError:
https://github.com/exasol/bucketfs-python/blob/main/exasol/bucketfs/_path.py#L450

The current ticket therefore proposes to

• either change the existing method in order to return an empty iterator
• or raise a more specific error and add a convenience method catching this error and returning an empty iterator