bug: No engine field in request body

[louis-menlo]

Problem Statement

I'm sending a chat/completions request to the cortex.cpp endpoints, setting up my daily use tools. The request is fully OpenAI compatible. I always receive an error response similar to this:

{
    "message": "No engine field in request body"
}

Feature Idea

Since the cortex.cpp manages to retrieve model information, it should select the engine accordingly. This eliminates the need for an extra engine field in the request, ensuring that 100% OpenAI-compatible products can utilize the endpoint.

[louis-menlo]

It always returns an empty response, regardless of how I modify the request body.

[gabrielle-ong]

@louis-jan can I verify this PR fixes this issue? cc @vansangpfiev

[louis-menlo]

Hi @gabrielle-ong, I tested the latest version, and it works now.