Fix bug where `yield from` is captured too greedily

Fix bug where `yield from` is captured too greedily

In the following piece of code:

```php
function from1234($x) {
  return $x;
}
function foo($x) {
  yield from1234($x);
}
```

The statement inside foo is taken as `yield from` `1234($x)`
which is neither the intent, nor even legal syntax for an fcall.

Do a lookahead for breaking non-label characters after the
`yield from` and only accept it if they occur.