isHistory 没被写过 只有这一个地方读了一次

[YitianJiang]

isPersist := utils.GetSwitchFromOptions(Options, "persistent")
switch pbData.SessionType {
case constant.SingleChatType:
	log.NewDebug(pbSaveData.OperationID, "msg_transfer chat type = SingleChatType", isHistory, isPersist)
	if **_isHistory_** {
		if msgKey == pbSaveData.RecvID {
			err := saveUserChat(pbData.RecvID, &pbSaveData)
			if err != nil {
				log.NewError(pbSaveData.OperationID, "single data insert to mongo err", err.Error(), pbSaveData.String())
				return
			}