Add check so that FlashIAP does not allocate memory on flash_init failure

[dustin-crossman]

Summary of changes

Adds a check to ensure FlashIAP does not allocate memory (with new[]) if a targets flash_init() call fails.

This fixes: #12439

Note: I did not add a similar check to the deinit to prevent calling delete[] on _page_buf if flash_free fails. There are a couple reasons for this:

1. If flash_init() succeeds but flash_free() fails _page_buf will be valid and should be deleted (though the underlying targets flash driver may be in an undefined state. This can't really be prevented at the FlashIAP level).
2. If flash_init() fails it is not valid to call FlashIAP::deinit (though it sounds like there is no documentation for that yet? Is that right @0xc0170 ?). If the user calls FlashIAP::deinit anyway it is safe to call delete[] on a null ptr.

Impact of changes

Migration actions required

Documentation

None

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Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

This can't really be tested programmatically since there is no way to modify a targets mbed_hal implementation during a test but I ran the mbed_hal-flash and mbed_drivers-flashiap tests under two different conditions.

Condition 1: pr/flashiap_fix branch with no changes:
mbed_hal-flash passes
mbed_drivers-flashiap passes

Condition 2: pr/flashiap_fix branch with flash_init() modified to always return failure:
mbed_hal-flash fails (as expected)
mbed_drivers-flashiap fails (as expected) but with no OOM error.

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Reviewers

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[ciarmcom]

@dustin-crossman, thank you for your changes.
@ARMmbed/mbed-os-core @ARMmbed/mbed-os-maintainers please review.

[evedon]

Astyle issue should be fixed but otherwise code change looks good.

Pull request has been modified.

[dustin-crossman]

@evedon Fixed up!

[0xc0170]

CI started

[0xc0170]

If flash_init() fails it is not valid to call FlashIAP::deinit (though it sounds like there is no documentation for that yet? Is that right @0xc0170 ?). If the user calls FlashIAP::deinit anyway it is safe to call delete[] on a null ptr.

Correct, I don't see any undefined behavor specified in this driver, yet.

[mbed-ci]

Test run: FAILED

Summary: 2 of 7 test jobs failed
Build number : 1
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_cloud-client-pytest
• jenkins-ci/mbed-os-ci_greentea-test

[0xc0170]

CI restarted

[mbed-ci]

Test run: FAILED

Summary: 1 of 7 test jobs failed
Build number : 2
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_cloud-client-pytest

[0xc0170]

Client restarted