fix: Improve error handling in file download API

[HynoR]

What this PR does / why we need it?

修复打开文件时，出现报错未提前return导致空指针报panic的问题。

Summary of your change

正确处理错误并提前 return 退出

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

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