Infinite loop when using Matcher.namedGroups

It seems that if the pattern matches an empty string, an infinite loop occurs when using Matcher.namedGroups, even if the matched input isn't an empty string. Here's a code example:

```
Pattern pattern = Pattern.compile("(?<first>A)?(?<second>B)?");
Matcher matcher = pattern.matcher("AB");
if(matcher.matches()) {
    matcher.namedGroups();
}
```