[FLINK-33502][network] Prevent DiskTierProducerAgent#getSegmentIdByIndexOfFirstBufferInSegment from throwing NPE when the task is released

[WencongLiu]

What is the purpose of the change

Prevent DiskTierProducerAgent#getSegmentIdByIndexOfFirstBufferInSegment from throwing NPE when the task is released.

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

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

[flinkbot]

CI report:

• 2b15892 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[WencongLiu]

If you have some free time, could you please take a look? Thank you 😊 @reswqa

[reswqa]

Thanks @WencongLiu for the fix, I left some comments, PTAL.

[reswqa]

Thanks for the update, I'm + 1 for this one. Could you please also align commit message with the title of this PR.

[WencongLiu]

Thanks for the update, I'm + 1 for this one. Could you please also align commit message with the title of this PR.

Done.