Check extension exists before calling hello route

[DarcyRaynerDD]

What does this PR do?

Changes logic for extension detection, to first check if the extension exists on disk. This is consistent with behavior in the node layer.

Motivation

Without this check, if a proxy is enabled on the lambda, it's possible that local host connections to the extension will be redirected through the proxy, incorrectly marking the extension as detected.

Testing Guidelines

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

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