concat failure in 0.20.16rc

[s-banach]

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

import polars as pl
A = pl.Series([None, 1]).sort().to_frame("x")
pl.concat([A, A, A])

Log output

PanicException: called `Option::unwrap()` on a `None` value

Issue description

Doesn't crash on 0.20.15.

Expected behavior

No error.

Installed versions

--------Version info---------
Polars:               0.20.16-rc.1
Index type:           UInt32
Platform:             Windows-10-10.0.19045-SP0
Python:               3.11.4 | packaged by conda-forge | (main, Jun 10 2023, 17:59:51) [MSC v.1935 64 bit (AMD64)]

----Optional dependencies----
adbc_driver_manager:  0.5.1
cloudpickle:          <not installed>
connectorx:           <not installed>
deltalake:            <not installed>
fastexcel:            0.9.1
fsspec:               2023.4.0
gevent:               <not installed>
hvplot:               <not installed>
matplotlib:           3.8.2
numpy:                1.25.2
openpyxl:             3.1.2
pandas:               2.2.0
pyarrow:              15.0.0
pydantic:             2.2.1
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           2.0.15
xlsx2csv:             0.8.1
xlsxwriter:           3.1.2

[nameexhaustion]

Can you provide the code that creates the data?

This is likely introduced by #15050, but I suspect the culprit is not in the PR itself. There seems to be a sorted flag somewhere that should not have been set.

[s-banach]

I have updated the example.