Fix bug in ASIO shutdown

[SeanTAllen]

Prior to this commit, when shutting down the ASIO subsystem, we ignored the result of our waiting to join on the ASIO thread's termination.

By ignoring the result, in cases where the join failed, we would continue doing ASIO shutdown related activities while the ASIO system was still running.

This was "not good".

[SeanTAllen]

@dipinhora is the interaction with the systematic testing asio shutdown ok with this change?

[ponylang-main]

Hi @SeanTAllen,

The changelog - fixed label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do.

Release notes are added by creating a uniquely named file in the .release-notes directory. We suggest you call the file 4548.md to match the number of this pull request.

The basic format of the release notes (using markdown) should be:

## Title

End user description of changes, why it's important,
problems it solves etc.

If a breaking change, make sure to include 1 or more
examples what code would look like prior to this change
and how to update it to work after this change.

Thanks.

[dipinhora]

@dipinhora is the interaction with the systematic testing asio shutdown ok with this change?

systematic testing shouldn't be impacted (i think) as it already works with how the asio shutdown process happens...

[dipinhora]

i'm not an expert on the failure conditions for ponyint_thread_join and whether that same thread might be able to be successfully ponyint_thread_join'd later on or not but this seems good to me..

[SeanTAllen]

successfully ponyint_thread_join'd later on or not but this seems good to me..

Unless I am completely misreading the docs that I refreshed myself on, that shouldn't be possible.