egg body 解析bug
问题机器egg环境：
```javascript
"egg": {
    "declarations": true
  },
  "dependencies": {
    "autocannon": "^7.9.0",
    "egg": "^2",
    "egg-redis": "^2.4.0",
    "egg-scripts": "^2",
    "tsc": "^2.0.4",
    "undici": "^5.7.0"
  },
  "devDependencies": {
    "autod": "^3",
    "autod-egg": "^1",
    "egg-bin": "^4",
    "egg-ci": "^2",
    "egg-mock": "^4",
    "eslint": "^8",
    "eslint-config-egg": "^12"
  },
  "engines": {
    "node": ">=16.0.0"
  },

```
问题复现：
post body 的字符串内容为json ` {"path":"\n"}`
传输过去的内容为` "{\"path\":\"\n\"}"`
在解析这个内容出现json解析错误，在springboot环境可解析正常，问题应该出现在egg http body 解析这块逻辑，报错如下。

```java
`2022-07-19 16:20:19,344 WARN 39558 [-/127.0.0.1/-/0ms POST /new] nodejs.SyntaxError: Unexpected token 
 in JSON at position 9, check bodyParser config
 in JSON at position 9, check bodyParser config
    at JSON.parse (<anonymous>)
    at parse (src/nodejs/release/node_modules/_co-body@6.1.0@co-body/lib/json.js:57:17)
    at AsyncFunction.module.exports [as json] (src/nodejs/release/node_modules/_co-body@6.1.0@co-body/lib/json.js:41:20)
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async parseBody (src/nodejs/release/node_modules/_koa-bodyparser@4.3.0@koa-bodyparser/index.js:100:14)
    at async bodyParser (src/nodejs/release/node_modules/_koa-bodyparser@4.3.0@koa-bodyparser/index.js:85:19)
    at async src/nodejs/release/node_modules/_koa-static-cache@5.1.4@koa-static-cache/index.js:39:63
    at async notfound (src/nodejs/release/node_modules/_egg@2.36.0@egg/app/middleware/notfound.js:5:5)
    at async meta (src/nodejs/release/node_modules/_egg@2.36.0@egg/app/middleware/meta.js:18:5)
status: 400
body: "{\"path\":\"\n\"}"
pid: 39558`

```