CThunk: Fix assertion when CThunk object is destroyed

[teijokinnunen]

In case the CThunk object is deleted without having called the
entry() function (and thus _entry is NULL), cthunk_free_real()
will fail with an assertion.

Description

Tested manually with a SPI object (containing a CThunk) that was created and deleted dynamically, using MBED OS 5.12.4. Before the change, deletion of the object caused an assert, after the change it works fine.

Pull request type

[ X ] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

Reviewers

Release Notes

[0xc0170]

Assert or MBED_ERROR ? I can see 141 line in CThunkBase is invoked if item is not found - is this case? I expected cthunk_free to take care of this "entry being null" but looks like it only checks free function pointer, not an argument.

[ciarmcom]

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

[teijokinnunen]

Assert or MBED_ERROR ? I can see 141 line in CThunkBase is invoked if item is not found - is this case? I expected cthunk_free to take care of this "entry being null" but looks like it only checks free function pointer, not an argument.

Right, it's this MBED_ERROR that gets triggered:
MBED_ERROR(MBED_MAKE_ERROR(MBED_MODULE_PLATFORM, MBED_ERROR_CODE_INVALID_ARGUMENT), "Tried to free invalid CThunkEntry");

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts