[bug] WinCred kr.Keys() return empty when kr.Set() doesn't call before

[Halimao]

I have set keyring:default:key1, keyring:default:key2 already, and can be found in windows Credential Manager. then test following code:

kr, err := keyring.Open(keyring.Config{
    AllowedBackends: []keyring.BackendType{keyring.WinCredBackend},
})
if err != nil {
    t.Fatal(err)
}
keys, err := kr.Keys()
if err != nil {
    t.Fatal(err)
}

it would return empty keys. but if I call kr.Set() before kr.Keys(), it would return keyring:default:key1 and keyring:default:key2

kr, err := keyring.Open(keyring.Config{
    AllowedBackends: []keyring.BackendType{keyring.WinCredBackend},
})
if err != nil {
    t.Fatal(err)
}
item1 := keyring.Item{
    Key:  "test3",
    Data: []byte("loose lips sink ships"),
}
err = kr.Set(item1)
if err != nil {
    t.Fatal(err)
}
keys, err := kr.Keys()
if err != nil {
    t.Fatal(err)
}

[Halimao]

kr, err := keyring.Open(keyring.Config{
    AllowedBackends: []keyring.BackendType{keyring.WinCredBackend},
})
if err != nil {
    t.Fatal(err)
}
key, err := kr.Get("key1")
if err != nil {
    t.Fatal(err)
}
t.Log(key)

will cause panic, it's because calling cred, err := wincred.GetGenericCredential(k.credentialName(key)) returns nil, nil without error, and cred is used for cred.CredentialBlob caused panic

func (k *windowsKeyring) Get(key string) (Item, error) {
	cred, err := wincred.GetGenericCredential(k.credentialName(key))
	if err != nil {
		if err == elementNotFoundError {
			return Item{}, ErrKeyNotFound
		}
		return Item{}, err
	}

	item := Item{
		Key:  key,
		Data: cred.CredentialBlob,
	}

	return item, nil
}