panic due to concurrent map writes about gowebdav HOT 8 CLOSED

package main

import (
	"log"
	"net/http"
	"net/http/httptest"
	"sync"

	"github.com/studio-b12/gowebdav"
	"golang.org/x/net/webdav"
)

func basicAuth(h http.Handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if user, passwd, ok := r.BasicAuth(); ok {
			if user == "user" && passwd == "password" {
				h.ServeHTTP(w, r)
				return
			}

			http.Error(w, "not authorized", 403)
		} else {
			w.Header().Set("WWW-Authenticate", `Basic realm="x"`)
			w.WriteHeader(401)
		}
	}
}

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/", basicAuth(&webdav.Handler{
		FileSystem: webdav.Dir("/"),
		LockSystem: webdav.NewMemLS(),
	}))

	server := httptest.NewServer(mux)
	defer server.Close()

	cli := gowebdav.NewClient(server.URL, "user", "password")

	var wg sync.WaitGroup

	for i := 0; i < 2; i++ {
		wg.Add(1)

		go func() {
			defer wg.Done()
			f, err := cli.ReadDir("/")
			log.Printf("f: %v err: %v", f, err)
		}()
	}

	wg.Wait()
}

╰─➤  go run -race repro                                                                                                                   1 ↵
==================
WARNING: DATA RACE
Read at 0x00c00011cf50 by goroutine 9:
  github.com/studio-b12/gowebdav.(*Client).req()
      /Users/jarek/Projects/gowebdav/requests.go:45 +0x1276
  github.com/studio-b12/gowebdav.(*Client).propfind()
      /Users/jarek/Projects/gowebdav/requests.go:94 +0x15a
  github.com/studio-b12/gowebdav.(*Client).ReadDir()
      /Users/jarek/Projects/gowebdav/client.go:164 +0x1fb
  main.main.func1()
      /Users/jarek/Projects/repro/main.go:48 +0x9f

Previous write at 0x00c00011cf50 by goroutine 8:
  github.com/studio-b12/gowebdav.(*Client).req()
      /Users/jarek/Projects/gowebdav/requests.go:54 +0xd48
  github.com/studio-b12/gowebdav.(*Client).propfind()
      /Users/jarek/Projects/gowebdav/requests.go:94 +0x15a
  github.com/studio-b12/gowebdav.(*Client).ReadDir()
      /Users/jarek/Projects/gowebdav/client.go:164 +0x1fb
  main.main.func1()
      /Users/jarek/Projects/repro/main.go:48 +0x9f

Goroutine 9 (running) created at:
  main.main()
      /Users/jarek/Projects/repro/main.go:46 +0x4de

Goroutine 8 (running) created at:
  main.main()
      /Users/jarek/Projects/repro/main.go:46 +0x4de