Handle case when context is too long

[dustinlacewell]

Unexpected chunk: {
  "error": {
    "message": "This model's maximum context length is 8192 tokens. However, your messages resulted in 10944 tokens. Please reduce the length of the messages.",
    "type": "invalid_request_error",
    "param": "messages",
    "code": "context_length_exceeded"
  }
}