BatchedParquetReader erroneously returns true for is_finished after the first get_batches call

[michaeleisel]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

For the following batched reading of a 10,000,000 row file, p.is_finished() returns true after just the first call to .next_batches. If, however, I just call .next_batches more and ignore p.is_finished() being true, it'll return more batches as I would expect it to.

fn main() {
    let mut p = ParquetReader::new(File::open("/path/to/test_data.parquet").unwrap()).set_low_memory(true).batched(100).unwrap();
    while !p.is_finished() {
        assert!(task::block_on(p.next_batches(1)).is_ok());
    }
}

Cargo.toml:

polars = { version = "0.37.*", features = ["lazy", "parquet", "ndarray", "async", "is_in", "polars-ops", "cloud", "streaming"] }
polars-io = { version = "0.37.*", features = ["lazy", "parquet", "ipc"] }

Log output

No response

Issue description

Expected behavior

It should return false for .is_finished until it's actually finished

Installed versions