Punycode mishandling by puny_decode/puny_encode

```
> urltools::puny_decode("xn--hxakfddc2amo8b.xn--qxam")
[1] "ελράδειγμα.ελράδειγμα"
> urltools::puny_decode("http://wwww.ελράδειγμα.ελ")
[1] "http://wwww.ελράδειγμα.ελ"
> urltools::puny_encode("ελράδειγμα.ελ")
[1] "xn--hxakfddc2amo8b.xn--qxam"
> urltools::puny_encode("xn--hxakfddc2amo8b.xn--qxam")
[1] "xn--xn--hxakfddc2amo8b-.xn--xn--qxam-"
```
