ARROW-15665: [C++] Fix error_is_null in strptime with invalid inputs

[rok]

As reported by @dragosmg the following:

StrptimeOptions options("%m/%d/%Y", TimeUnit::MICRO, /*error_is_null=*/true);
std::string input2 = R"(["5-1-2020", "12/13/1900"])";
std::string output2 = R"([null, "1900-12-13"])";
Strptime(input2, options)

Would cause:

Expected:
  [
    null,
    1900-12-13 00:00:00.000000
  ]
Actual:
  [
    null,
    1970-01-01 00:00:00.000000
  ]

This was due to out_data pointer not updating on failed parsing.

This change fixes the issue and adds a test.

[rok]

@lidavidm I'm a bit embarrassed by this one :)

[lidavidm]

Ah, d'oh, we both missed this one. Thanks for fixing this.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-15665

[ursabot]

Benchmark runs are scheduled for baseline = f4dfd6c and contender = 6a0770c. 6a0770c is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Finished ⬇️0.38% ⬆️0.13%] test-mac-arm
[Finished ⬇️0.36% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️1.02% ⬆️0.3%] ursa-thinkcentre-m75q
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java