httpx.Parse returns 500 error if all arguments have defaults and no value submitted

[Cwt-ting]

Describe the bug
提交参数只有2个可选时，2个参数都不传的情况下 会报 httpx.Parse 500 解析错误

To Reproduce
Steps to reproduce the behavior, if applicable:

1. The code is

   	var req types.ApplyFriendsListReq
    	if err := httpx.Parse(r, &req); err != nil {
    		httpx.Error(w, err)
    		return
    	}

2. The error is

**Expected behavior**
A clear and concise description of what you expected to happen.

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Environments (please complete the following information):**
- OS: [e.g. Linux]
- go-zero version [e.g. 1.2.1]
- goctl version [e.g. 1.2.1, optional]

**More description**
Add any other context about the problem here.

[Kevin Wan]

I cannot reproduce this issue, check the code here: https://github.com/kevwan/zero-issues/tree/main/1197

[Cwt-ting]

The problem from the definition of error handling