bug: api7-lua-resty-http包在解析带有Expect的响应时不符合RFC2616规范

### Issue description

apisix作为中间代理层，通过ext-plugin-post-resp扩展使用Java插件，代理转发客户端请求到上游服务。其中客户端发起HTTP请求头中包含Expect属性，后端服务在接收到Expect属性时，分别响应```HTTP/1.1 100 Continue ```回应支持，或者```HTTP/1.1 417 Expectation Failed```。当Response包含了响应头信息（例如Server属性）后apisix会出现```failed to request: couldn't parse HTTP version from response status line: ```的错误，客户端收到502的请求响应。

就如上业务场景，参考RFC2616规范内容：

在RFC2616规范中
```4.4 Message Length```内容如下：
```
1.Any response message which "MUST NOT" include a message-body (such
as the 1xx, 204, and 304 responses and any response to a HEAD
request) is always terminated by the first empty line after the
header fields, regardless of the entity-header fields present in
the message.
```
```6 Response```内容如下：
```
After receiving and interpreting a request message, a server responds
with an HTTP response message.

Response = Status-Line ; Section 6.1
*(( general-header ; Section 4.5
| response-header ; Section 6.2
| entity-header ) CRLF) ; Section 7.1
CRLF
[ message-body ] ; Section 7.2
```
结论：在请求头包含```Expect```时，响应码100允许返回```general-header```和```response-header```信息。

ext-plugin-post-resp 插件实现依赖http.lua代码如下：
```
local function _handle_continue(sock, body)
-- _receive_status 方法中会读取1行数据。即：HTTP/1.1 100 Continue
local status, version, reason, err = _receive_status(sock) --luacheck: no unused
if not status then
return nil, nil, err
end

-- Only send body if we receive a 100 Continue
if status == 100 then
-- 当响应包含Header信息时会被读取到，后续的解析就会因此出错
local ok, err = sock:receive("*l") -- Read carriage return
if not ok then
return nil, nil, err
end
_send_body(sock, body)
end
return status, version, err
end
```
建议代码如下：
```
local function _handle_continue(sock, body)
local status, version, reason, err = _receive_status(sock) --luacheck: no unused
if not status then
return nil, nil, err
end

-- Only send body if we receive a 100 Continue
if status == 100 then
-- 读取到空行后再做后续处理
repeat
local ok, err = sock:receive("*l") -- Read carriage return
if not ok then
return nil, nil, err
end
until (ok and #ok == 0)
_send_body(sock, body)
end
return status, version, err
end
```

### Environment
* apisix V3.2
* apisix-java-plugin-runner

### Minimal test code / Steps to reproduce the issue

1. Postman 通过POST请求接口，Header头中增加Expect: 100-continue属性
2. Tomcat 容器下返回```HTTP/1.1 100 Continue ```
3. Undertow 容器下返回（Undertow官方在2.2.21.Final版本修改并去掉了Content-Length的属性）
```
HTTP/1.1 100 Continue
Content-Length: 0
```

### What's the actual result? (including assertion message & call stack if applicable)
当出现类似Undertow带有Content-Length的属性响应时，apisix解析报头时会报错

### What's the expected result?
正常处理并返回客户端200