Description:
------------
@bwoebi came up with this reduction of oss-fuzz #25697 a while ago, report a bug to make sure it doesn't get lost in a chat log...

Test script:
---------------
<?php

function gen() {
    yield 0;
    yield from gen();
}

function bar($gen) {
    yield from $gen;
}

$gen = gen();
$a = bar($gen);
$b = bar($gen);
$a->rewind();
$b->rewind();
$a->next();
unset($gen);
unset($a);
unset($b);