fix: correctly cleaning up the websocket stream

[zhouzh1]

Issue #, if available:
None

Description of changes:
The issue we're suffering from:
Currently we found there're many crashes in our iOS app which are related to the AWSIoT lib when it's cleaning up the websocket streams, after dig into the relevant source code, I think the possible reason for those crashes is that the lib code doesn't put enough consideration for the situation where the created websocket stream is shared by mutiple threads, meanwhile, more than one thread have the method to perform the cleaning job for that websocket stream, and moreover, they don't check the stream status, that would cause the same websocket stream to be cleaned more than one time, then the app crash happens. The below screenshot shows some crash reports.

The changes implemented in this PR

• Imposing stricter status check before cleaning the associated stream object, to ensure the stream will only be cleaned one time.

Check points:

• Added new tests to cover change, if needed
• All unit tests pass
• All integration tests pass
• Updated CHANGELOG.md
• Documentation update for the change if required
• PR title conforms to conventional commit style

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[zhouzh1]

@awsmobilesdk Hi guys, anyone can help take a look at this PR? Currently the corresponding issues are causing many app crashes, but I am not sure if my change makes sense, please help confirm, thanks.

[zhouzh1]

@ruisebas @thisisabhash Could you help take a look at this PR?

[ruisebas]

Hi @zhouzh1, thanks for opening this PR!

Unfortunately, the validations you've added will not prevent concurrency issues/crashes, since they can still be accessed by multiple threads at the same time.

However, we've recently added several concurrency checks in version 2.38.1 that might prevent your crashes. Would you mind checking that version up?

If after upgrading you're still getting crashes, please submit an issue and provide the full symbolicated crashlog and we'll take a look.

Thanks!