fix: ignore allowedOrigins config for undefined origin header to ensure correct CORS behavior

[tanlethanh]

Hi Flowise team,

I discovered that after configuring allowedDomains (as dynamic CORS) for a chatflow, It checks my origin header even if it is undefined. The request might be sent from a proxy server or postman and usually sends requests with undefined origin.

The error I got when requesting to /api/v1/prediction from postman or curl was:

{
    "statusCode": 500,
    "success": false,
    "message": "Invalid URL",
    "stack": {}
}

[HenryHengZJ]

thank you @tanlethanh !