[BugFix] fix NPE in case of LDAP user (backport #65843)

[mergify]

Why I'm doing:

What I'm doing:

2025-11-21 11:49:15.954+08:00 WARN (starrocks-taskrun-pool-9|6750) [TaskRunExecutor.lambda$executeTaskRun$0():67] failed to execute TaskRun. 
java.lang.NullPointerException: null 	
at com.starrocks.epack.authorization.AuthorizationMgrEpack.getRoleIdsByUserUnlocked(AuthorizationMgrEpack.java:75) ~[starrocks-fe.jar:?] 	
at com.starrocks.privilege.AuthorizationMgr.getRoleIdsByUser(AuthorizationMgr.java:1422) ~[starrocks-fe.jar:?] 	
at com.starrocks.scheduler.TaskRun.switchUser(TaskRun.java:278) ~[starrocks-fe.jar:?] 	
at com.starrocks.scheduler.TaskRun.buildTaskRunConnectContext(TaskRun.java:248) ~[starrocks-fe.jar:?] 	
at com.starrocks.scheduler.TaskRun.executeTaskRun(TaskRun.java:296) ~[starrocks-fe.jar:?] 	
at com.starrocks.scheduler.TaskRunExecutor.lambda$executeTaskRun$0(TaskRunExecutor.java:60) ~[starrocks-fe.jar:?] 	
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1700) ~[?:?] 	
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[?:?] 	
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[?:?] 	
at java.lang.Thread.run(Thread.java:829) ~[?:?]

The switchUser function depends on the ConnectContext.get(), which is used for LDAP user, but this condition is not guaranteed by TaskRun.buildTaskRunConnectContext.

It only occurs in enterprise-version but not OSS.

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.0
  • 3.5
  • 3.4
  • 3.3

---

This is an automatic backport of pull request #65843 done by [Mergify](https://mergify.com).

[mergify]

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