[fix](publish) Avoid NPE for force-finished publish task

[deardeng]

FE publish can loop on:

java.lang.NullPointerException: Cannot invoke
"java.util.Map.containsKey(Object)" because the return value of
"PublishVersionTask.getSuccTablets()" is null
at DatabaseTransactionMgr.checkReplicaContinuousVersionSucc(...)
at DatabaseTransactionMgr.finishCheckQuorumReplicas(...)
at DatabaseTransactionMgr.finishTransaction(...)

PublishVersionTask starts with succTablets == null, but
AgentTaskCleanupDaemon.removeInactiveBeAgentTasks can force-finish an
in-flight task with setFinished(true) without ever calling setSuccTablets.
That leaves a finished task whose getSuccTablets() still returns null.

MasterImpl.finishPublishVersion is only a theoretical source here:
BE task_worker_pool.cpp unconditionally sets succ_tablets on the finish
request, so that path currently receives at worst an empty map.

Fix this on both sides:

• default PublishVersionTask.succTablets to an empty map and coerce null
• guard the call site before containsKey(tabletId)

Add FE unit coverage and a regression suite for BE-down publish cleanup.

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[deardeng]

run buildall

[deardeng]

run buildall