Fix segmentation fault when using setters or getters that are not defined

[rolftimmermans]

Currently the following scenario aborts with a segmentation fault:

exports.Set("Text", DefineClass(env, "Test", {
    InstanceAccessor("readonly_prop", &Test::GetReadonlyProp, nullptr),
}));

new Test().readonly_prop = 1;

This PR fixes that scenario by checking for a null getter/setter and setting the property descriptor accordingly. Includes a test case for readonly properties.

I had to modify the test runner to correctly report SIGSEGV in order for it to actually fail the tests.

[mhdawson]

Sorry I've not had a chance to check this out yet. I'm out at Node Interactive this week but will try to get to it when I have spare time.

[mhdawson]

Seems like this PR #159 is fixing the same/similar problem. That PR does not seem to have the change you needed to make sure the test failed. Can you take a look at that PR and then potentially revise this one to have what would still be needed after that ?

[rolftimmermans]

I fixed the conflicts, added a write only test and fixed a segfault that was caused by a missing SuppressDestruct.

If the other PR is merged we can still update the segfault logic and fix of course.

[mhdawson]

Ok, my plan is to land the other PR, ask you to rebase and then I can go ahead and land this one. Sorry for taking so long to review this one....

[mhdawson]

Ok other PR has landed, if you can rebase that would be great.

[rolftimmermans]

👍 done

[mhdawson]

LGTM

[mhdawson]

Landed as 22be609