dynamic_modules: don't call on_http_filter_destroy_ if filter is null

[bplotnick]

I tested dynamic modules from rust and was getting a segfault. I noticed that drop was getting called twice. It turns out that onDestroy gets called twice. The right solution here is probably to prevent onDestroy() from being called twice... but barring that, this change works.

Commit Message: dynamic_modules: don't call on_http_filter_destroy_ if filter is null
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[bplotnick]

/assign @mathetake

[repokitteh-read-only]

bplotnick is not allowed to assign users.

🐱

Caused by: a #37899 (comment) was created by @bplotnick.

see: more, trace.

[mathetake]

thank you for finding this out.. but i am still not sure when does this happen. Can you add a test case in filter_test.cc to cover this case as well as a basic integration test?

[bplotnick]

thank you for finding this out.. but i am still not sure when does this happen. Can you add a test case in filter_test.cc to cover this case as well as a basic integration test?

i'm not sure 🫤. I can't think of why it would, but I know it happens and segfaults when i use it and that this PR fixes the issue. I will take a look at reproing with an integration test though.

[bplotnick]

@mathetake I was able to repro the issue with an integration test and confirmed that this PR fixes things. I still don't know why it is happening though.

If you want to repro on this branch as well, you can comment out https://github.com/envoyproxy/envoy/pull/37899/files#diff-c3823903be9c28689c8502bf6bbcc3ec6e771b6903b4cdf2317f99c82ce679caR21-R23 and run bazel test //test/extensions/dynamic_modules/http:integration_test

[mathetake]

cool, thank you for adding the integration test that hits the case!

[mathetake]

LGTM. Thank you for scaffolding the integration test. Deferring to @mattklein123