[computation-governance][application-manager] fix null pointer exception in engine reuse metrics update

[v-kkhuang]

What is the purpose of the change

This PR fixes a null pointer exception that occurs during engine creation and reuse metrics update, improving system stability.

Related issues/PRs

Related issues: none
Related pr:none

Brief change log

• Fix null pointer exception in DefaultEngineCreateService
• Fix null pointer exception in DefaultEngineReuseService

Checklist

• I have read the Contributing Guidelines on pull requests.
• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the Linkis mailing list first)
• If this is a code change: I have written unit tests to fully verify the new behavior.