pl.concat_list() can cause explode() to throw a shape error

[jaschn]

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

df = pl.DataFrame(
	{
		"cl1": [[0], [0]],
		"cl2": [[0], [0]],
	}
)

df_row_1 = df[1] # index 0 works and any others fail
df_row_1 = df_row_1.select(
		pl.col("cl1"),
		pl.concat_list(pl.col("cl2")) # without pl.concat it works as well
	)

df_row_1.explode(pl.all())

Log output

---------------------------------------------------------------------------
ShapeError                                Traceback (most recent call last)
Cell In[6], line 16
     10 df_row_1 = df[1]
     11 df_row_1 = df_row_1.select(
     12 		pl.col("cl1"),
     13 		pl.concat_list(pl.col("cl2"))
     14 	)
---> 16 df_row_1.explode(pl.all())

File ~/miniconda3/envs/x/lib/python3.12/site-packages/polars/dataframe/frame.py:7193, in DataFrame.explode(self, columns, *more_columns)
   7136 def explode(
   7137     self,
   7138     columns: str | Expr | Sequence[str | Expr],
   7139     *more_columns: str | Expr,
   7140 ) -> DataFrame:
   7141     """
   7142     Explode the dataframe to long format by exploding the given columns.
   7143 
   (...)
   7191     └─────────┴─────────┘
   7192     """
-> 7193     return self.lazy().explode(columns, *more_columns).collect(_eager=True)

File ~/miniconda3/envs/x/lib/python3.12/site-packages/polars/lazyframe/frame.py:1816, in LazyFrame.collect(self, type_coercion, predicate_pushdown, projection_pushdown, simplify_expression, slice_pushdown, comm_subplan_elim, comm_subexpr_elim, no_optimization, streaming, background, _eager, **_kwargs)
   1813 # Only for testing purposes atm.
   1814 callback = _kwargs.get("post_opt_callback")
-> 1816 return wrap_df(ldf.collect(callback))

ShapeError: exploded columns must have matching element counts

Issue description

When indexing the non first row, having a list column and concatenating a list column the following explode() can fail with a shape error

Expected behavior

import polars as pl

df = pl.DataFrame(
	{
		"cl1": [[0], [0]],
		"cl2": [[0], [0]],
	}
)

df_row_1 = df[1]
df_row_1 = df_row_1.select(
		pl.col("cl1"),
		pl.col("cl2")
	)

print(df_row_1.explode(pl.all()))

df_row_0 = df[0]
df_row_0 = df_row_0.select(
		pl.col("cl1"),
		pl.concat_list(pl.col("cl2"))
	)

print(df_row_0.explode(pl.all()))

shape: (1, 2)

cl1	cl2
i64	i64
0	0

shape: (1, 2)

cl1	cl2
i64	i64
0	0

Installed versions

--------Version info---------
Polars:               0.20.25
Index type:           UInt32
Platform:             Linux-5.15.146.1-microsoft-standard-WSL2-x86_64-with-glibc2.35
Python:               3.12.2 | packaged by conda-forge | (main, Feb 16 2024, 20:50:58) [GCC 12.3.0]

----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          3.0.0
connectorx:           <not installed>
deltalake:            <not installed>
fastexcel:            <not installed>
fsspec:               2024.3.1
gevent:               <not installed>
hvplot:               <not installed>
matplotlib:           3.8.4
nest_asyncio:         1.6.0
numpy:                1.26.4
openpyxl:             <not installed>
pandas:               2.2.1
pyarrow:              15.0.2
pydantic:             <not installed>
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           <not installed>
torch:                2.2.2+cu121
xlsx2csv:             <not installed>
xlsxwriter:           <not installed>