nodeaccess_nodereference_calculate_grants trapped in dead loop

After hours of tracing, I found the problem: the $parent_reference was unset to null after a child iteration is done, which causes the next child to be parent-less.

The fix is really simple, just move the assignment of $parent_reference into the operation processing loop:

foreach ($operations as $operation) {
// move into this loop
$parent_reference = $reference;