cannot get request.param if request.body lacks `=`
```nim
import uri, httpclient

let data = {
  "name": "",
  "email": "aaa@example.com"
}
echo data.encodeQuery()
>> name&email=aaa%40example.com

var client = newHttpClient()
client.headers = newHttpHeaders({"Content-Type": "application/x-www-form-urlencoded"})
discard client.post("/", body=data.encodeQuery())
```
If set data in request.body, Jester cannot parse query because query style is not same `key=value`

```nim
# in Jester
echo request.params
>> {"name&email": "aaa@example.com"}

# expected output
>> {"name": "", "email": "aaa@example.com"}
```
