Fix: Return HTTP 404 when file does not exist

[mahmoud-40]

Pull Request

Description

This PR adds a check to verify whether the requested file exists before attempting to access it. If the file does not exist, the API now returns an HTTP 404 Not Found error instead of failing with an internal server error.

Fixes #392

How Has This Been Tested?

• Extended existing test cases to cover scenarios where the requested file does not exist.
• Verified that the new checks do not break existing functionality

If your changes affect data processing, have you plotted any changes? i.e. have you done a quick sanity check?

• Data processing is not affected, as this change only modifies error handling.

Checklist:

• My code follows OCF's coding style guidelines
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked my code and corrected any misspellings

[peterdudfield]

@all-contributors please add @mahmoud-40 for code

[allcontributors]

@peterdudfield

I've put up a pull request to add @mahmoud-40! 🎉