`req.Bin[sepIndex+1:]` has an out-of-bounds error

[DoubleBirdsU]

An out-of-bounds situation occurs in the file llm/go-client/frontend/handlers/chat.go. seqIndex+1 is executed directly without judging the length, resulting in an out-of-bounds error.

	sepIndex := strings.Index(",", req.Bin)

	messages := h.ctxManager.GetHistory(ctxID)
	messages = append(messages, &chat.ChatMessage{
		Role:    "human",
		Content: req.Message,
		Bin:     []byte(req.Bin[sepIndex+1:]),
	})