Description:
------------
Using '*' to reference a block previously defined with '&' causes core dumps and "zend_mm_heap corrupted" messages.

Reproduce code:
---------------
var_dump(syck_load("
a: &b
  c: x

d: *b
"));

Expected result:
----------------
array(2) {
  ["a"]=>
  array(1) {
    ["c"]=>
    string(1) "x"
  }
  ["d"]=>
  array(1) {
    ["c"]=>
    string(1) "x"
  }
}


Actual result:
--------------
Segmentation fault (core dumped)