[pulsar-client-cpp] Fix for crash in Producer destructor

[heronr]

Motivation

This change fixes a crash I encountered when the destructor of the Producer is called.

Modifications

The ProducerStatsBasePtr is now declared in the header after the ExecutorServicePtr to ensure that it is destroyed before the ExecutorService. This is because the destructor of ProducerStatsImpl will attempt to cancel its outstanding DeadlineTimer which will then dereference the now destroyed ExecutorService and cause an exception.

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API: no
• The schema: no
• The default values of configurations: no
• The wire protocol: no
• The rest endpoints: no
• The admin cli options: no
• Anything that affects deployment: no

Documentation

• Does this pull request introduce a new feature? no

[merlimat]

I think this should already have been fixed in #6226. Can you double check?

[heronr]

Yes, you are right. That change will also result in fixing the crash I found. I'll close out this PR.