Behaviour of calling matches() and then find() doesn't match java.util.regex

In the following example, the behaviour of re2j doesn't match the behaviour of `java.util.regex`.

With `java.util.regex`, calling `matches()` and then `find()` advances to a second match (which doesn't exist), so it throws an `IllegalStateException`.

```java
public class T {
public static void main(String[] args) {
String pattern = "([1-5][0-9]{2})-([1-5][0-9]{2})";
String input = "201-299";
{
System.err.println("> re2j");
try {
var p = com.google.re2j.Pattern.compile(pattern);
var m = p.matcher(input);
if (m.matches()) {
m.find();
System.err.println(
"match: " + Integer.parseInt(m.group(1)) + " - " + Integer.parseInt(m.group(2)));
}
} catch (Exception e) {
System.err.println(e.getClass() + " " + e.getMessage());
}
}
{
System.err.println("> java.util.regex");
try {
var p = java.util.regex.Pattern.compile(pattern);
var m = p.matcher(input);
if (m.matches()) {
m.find(); // java.util.regex reports a match if the extra call to find() is removed
System.err.println(Integer.parseInt(m.group(1)) + " - " + Integer.parseInt(m.group(2)));
}
} catch (Exception e) {
System.err.println(e.getClass() + " " + e.getMessage());
}
}
}
}
```

```
> re2j
match: 201 - 299
> java.util.regex
class java.lang.IllegalStateException No match found
```