[C++] Cast segfaults on unsupported cast from list<binary> to utf8

[asfimport]

Was messing around with some nested arrays and found a pretty easy to reproduce segfault:

Python 3.7.6 | packaged by conda-forge | (default, Jan  7 2020, 22:33:48)
[GCC 7.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np, pyarrow as pa
>>> pa.__version__
'0.16.0'
>>> np.__version__
'1.18.1'
>>> x=[np.array([b'a',b'b'])]
>>> a = pa.array(x,pa.list_(pa.binary()))
>>> a
<pyarrow.lib.ListArray object at 0x7fd948b108a0>
[
  [
    61,
    62
  ]
]
>>> a.cast(pa.string())
Segmentation fault

I don't know if that cast makes sense, but I left the checks on, so I would not expect a segfault from it.

Reporter: Daniel Nugent / @nugend
Assignee: Krisztian Szucs / @kszucs

PRs and other links:

• GitHub Pull Request #6738

_{Note: This issue was originally created as ARROW-8070. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Thanks. The code definitely should not segfault

[asfimport]

Neal Richardson / @nealrichardson:
@kszucs see also https://issues.apache.org/jira/browse/ARROW-8025

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 6738
#6738