Possible goroutines leak

Hi!

I found some issue while using this package. Seems NewClient creation leads to goroutines leak. Could be reproduced on the simple request:

package main

import (
    "fmt"
    "runtime"

    "alexejk.io/go-xmlrpc"
)

func request() {
    client, err := xmlrpc.NewClient("https://bugzilla.mozilla.org/xmlrpc.cgi")
    if err != nil {
        panic(err)
    }
    defer client.Close()
    result := &struct {
        BugzillaVersion struct {
            Version string
        }
    }{}
    _ = client.Call("Bugzilla.version", nil, result)
    fmt.Printf("Version: %s\n", result.BugzillaVersion.Version)
}

func main() {
    for i := 0; i < 10; i++ {
        request()
        fmt.Printf("NumGoroutine: %d\n", runtime.NumGoroutine())
    }
}

Output:

Version: 20220119.1
NumGoroutine: 3
Version: 20220119.1
NumGoroutine: 4
Version: 20220119.1
NumGoroutine: 5
Version: 20220119.1
NumGoroutine: 6
Version: 20220119.1
NumGoroutine: 7
Version: 20220119.1
NumGoroutine: 8
Version: 20220119.1
NumGoroutine: 10
Version: 20220119.1
NumGoroutine: 10
Version: 20220119.1
NumGoroutine: 11
Version: 20220119.1
NumGoroutine: 12

I tried to find the root cause myself, but have no results yet.

alexejk / go-xmlrpc

Possible goroutines leak #52