[fix](load) fix s3 load check failed when no source file found

[liaoxin01]

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #55498

Problem Summary:

When importing a file via S3 load, if the file does not exist on S3, the load will report an error: label has already been used.

2025-09-22 23:00:57,177 WARN (pending-load-task-scheduler-pool-0|483) [LoadTask.exec():110] LOAD_JOB=1758553246283, error_msg={Unexpected failed to execute load task}
java.lang.IllegalStateException: null
at com.google.common.base.Preconditions.checkState(Preconditions.java:499) ~[guava-33.2.1-jre.jar:?]
at org.apache.doris.nereids.load.NereidsLoadingTaskPlanner.plan(NereidsLoadingTaskPlanner.java:146) ~[doris-fe.jar:1.2-SNAPSHOT]
at org.apache.doris.load.loadv2.LoadLoadingTask.init(LoadLoadingTask.java:138) ~[doris-fe.jar:1.2-SNAPSHOT]
at org.apache.doris.load.loadv2.BrokerLoadJob.createTask(BrokerLoadJob.java:274) ~[doris-fe.jar:1.2-SNAPSHOT]
at org.apache.doris.load.loadv2.BrokerLoadJob.createLoadingTask(BrokerLoadJob.java:311) ~[doris-fe.jar:1.2-SNAPSHOT]
at org.apache.doris.load.loadv2.BrokerLoadJob.onPendingTaskFinished(BrokerLoadJob.java:204) ~[doris-fe.jar:1.2-SNAPSHOT]
at org.apache.doris.load.loadv2.BrokerLoadJob.onTaskFinished(BrokerLoadJob.java:163) ~[doris-fe.jar:1.2-SNAPSHOT]
at org.apache.doris.load.loadv2.LoadTask.exec(LoadTask.java:102) ~[doris-fe.jar:1.2-SNAPSHOT]
at org.apache.doris.task.MasterTask.run(MasterTask.java:31) ~[doris-fe.jar:1.2-SNAPSHOT]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539) ~[?:?]
at java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[?:?]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) ~[?:?]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) ~[?:?]
at java.lang.Thread.run(Thread.java:833) ~[?:?]

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

[Thearas]

Thank you for your contribution to Apache Doris.
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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?

[liaoxin01]

run buildall

[liaoxin01]

run buildall

[hello-stephen]

FE UT Coverage Report

Increment line coverage 0.00% (0/2) 🎉
Increment coverage report
Complete coverage report

[hello-stephen]

FE Regression Coverage Report

Increment line coverage 100.00% (2/2) 🎉
Increment coverage report
Complete coverage report

[dataroaring]

LGTM

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.

[sollhui]

LGTM