fix: return error if file's missing

[zkpepe]

Pull Request type

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• Bugfix
• Feature
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Description

was exiting 0 even when the file didn’t exist — fixed that

Related Issues

n/a

Testing Performed

manually tested with and without the file — exit codes behave as expected now

Checklist

• I have performed a self-review of my own code.
• The tests pass successfully with cargo test.
• The code was formatted with cargo fmt.
• The code compiles with no new warnings with cargo build --release and cargo build --release --features runtime-benchmarks.
• The code has no new warnings when using cargo clippy.
• If this change affects documented features or needs new documentation, I have created a PR with a documentation update.