Cannot use with_context with output of scan_* functions

[erinov1]

Polars version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of Polars.

Issue description

The following raises an error:

import polars as pl

df1 = pl.LazyFrame({"A": [1]})
pl.DataFrame({"B": [1]}).write_csv("test.csv")

# This fails with PanicException: called `Option::unwrap()` on a `None` value
df1.with_context(pl.scan_csv("test.csv")).collect()

# This succeeds
df1.with_context(pl.scan_csv("test.csv").collect().lazy()).collect()

# Reversing the order also succeeds 
pl.scan_csv("test.csv").with_context(df1).collect()

The same error arises for scan_parquet and scan_ipc.

Reproducible example

import polars as pl

df1 = pl.LazyFrame({"A": [1]})
pl.DataFrame({"B": [1]}).write_csv("test.csv")

# This fails with PanicException: called `Option::unwrap()` on a `None` value
df1.with_context(pl.scan_csv("test.csv")).collect()

Expected behavior

Code should run regardless of the source of the lazyframe.

Installed versions

--------Version info---------
Polars:      0.17.15
Index type:  UInt32
Platform:    macOS-13.2-arm64-arm-64bit
Python:      3.11.1 (main, Feb  8 2023, 16:32:14) [Clang 14.0.0 (clang-1400.0.29.202)]

----Optional dependencies----
numpy:       1.23.5
pandas:      1.5.3
pyarrow:     11.0.0
connectorx:  <not installed>
deltalake:   <not installed>
fsspec:      2023.1.0
matplotlib:  3.7.0
xlsx2csv:    <not installed>
xlsxwriter:  <not installed>

[daviskirk]

I have this as well, interestingly only for polars > 0.19.6. Since this issue is older I'm not sure if it's really the same issue, or if #12416 also came up in newer versions.

[stinodego]

LazyFrame.with_context will be deprecated with the release of 1.0.0 (#16860). We will not fix any bugs associated with it.

Please use pl.concat(..., how="horizontal") instead to combine LazyFrames into a single context.