Iteration over a prefix with a single IP does not work

[rrb3942]

If you call ipaddr.Parse with input that is only a single IP (127.0.0.1, 127.0.0.1/32) the supplied cursor will not return any entries via Next(). Getting the value via First() works fine.

I believe Next() should return the first, and only entry, and then return nil.

I am parsing a mix of single hosts and networks both in CIDR notation and noticed that anything with a /32 prefix was being dropped because of Next() returning nil immediately.

Here is an example program to show the issue.

https://play.golang.org/p/xZEOyiLCXYN

`package main

import (
"fmt"
"github.com/mikioh/ipaddr"
)

func printIPs(ip string) {
cursor, err := ipaddr.Parse(ip)
if err != nil {
fmt.Println(err)
} else {
fmt.Println(cursor.Pos(), cursor.First(), cursor.Last(), cursor.List())
fmt.Println("First is: ", cursor.First().IP.String())
fmt.Println("All Members:")
for pos := cursor.Next(); pos != nil; pos = cursor.Next() {
fmt.Println(pos.IP.String())
}
}
}

func main() {
printIPs("192.168.168.77/32")
printIPs("127.0.0.1/32")
printIPs("127.0.0.0/29")
}
`