[fix][client] Prevent NPE when seeking with null topic in TopicMessageId

[3pacccccc]

Motivation

This PR addresses a potential NullPointerException (NPE) that could occur when calling the seek() method with a TopicMessageIdImpl that has a null topic.

Modifications

1. Added null check for the owner topic in MultiTopicsConsumerImpl.java before attempting to access it
2. Added comprehensive test case in SubscriptionSeekTest.java to verify the fix:
   • Creates a partitioned topic
   • Attempts to seek using a TopicMessageIdImpl with null topic
   • Verifies the proper exception is thrown with a clear error message

Verifying this change

• [x] Make sure that the change passes the CI checks.

If the box was checked, please highlight the changes

• [ ] Dependencies (add or upgrade a dependency)
• [ ] The public API
• [ ] The schema
• [ ] The default values of configurations
• [ ] The threading model
• [ ] The binary protocol
• [ ] The REST endpoints
• [ ] The admin CLI options
• [ ] The metrics
• [ ] Anything that affects deployment

Documentation

• [ ] doc
• [ ] doc-required
• [x] doc-not-needed
• [ ] doc-complete

Matching PR in forked repository

PR in forked repository: https://github.com/3pacccccc/pulsar/pull/8