list.arg_min() now returns 0 instead of null on an empty sub-list

[sorhawell]

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

in py-polars 0.18.5

pl.select( pl.lit(pl.Series([["a"],[]]))).with_columns(pl.all(),pl.all().list.arg_min().alias("arg_min"
),pl.all().list.arg_max().alias("arg_max"))
shape: (2, 3)
┌───────────┬─────────┬────────────┐
│           ┆ arg_min ┆ arg_max    │
│ ---       ┆ ---     ┆ ---        │
│ list[str] ┆ u32     ┆ u32        │
╞═══════════╪═════════╪════════════╡
│ ["a"]     ┆ 0       ┆ 0          │
│ []        ┆ 0       ┆ 4294967295 │
└───────────┴─────────┴────────────┘

Issue description

Noticed when bumping r-polars dependency to rust-polars 0.30.0 -> 0.32.0.

arg_min() now returns 0 instead of null on empty sub-list. However an empty list has zero length and there would be no first element to point to.

Expected behavior

as from rust-polars 0.30.0

pl.select( pl.lit(pl.Series([["a"],[]]))).with_columns(pl.all(),pl.all().list.arg_min().alias("arg_min"
),pl.all().list.arg_max().alias("arg_max"))
shape: (2, 3)
┌───────────┬─────────┬────────────┐
│           ┆ arg_min ┆ arg_max    │
│ ---       ┆ ---     ┆ ---        │
│ list[str] ┆ u32     ┆ u32        │
╞═══════════╪═════════╪════════════╡
│ ["a"]     ┆ 0       ┆ 0          │
│ []        ┆ Null       ┆ Null │
└───────────┴─────────┴────────────┘

in upcomming r-polars

### Installed versions

<details>

as of py-polars 0.18.5

</details>

[reswqa]

This is fixed in #10716 and can be closed. :)