server: fix SSE and OpenAI compatibility for error messages when streaming#16109

ngxson merged 2 commits intoggml-org:masterggml-org/llama.cpp:masterfrom

BenjaminBruenau:fix/server/sse-spec-error-messages-compatibilityBenjaminBruenau/llama.cpp:fix/server/sse-spec-error-messages-compatibilityCopy head branch name to clipboard