Description:
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The fourth parameter of xdiff_string_patch() $error should return failed hunks of the patch, but nothing is returned.

Will add PR later.

Test script:
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<?php
$str = "123\n456\n";
$patch = "@@ -1,2 +1,3 @@\n 789\n+012\n 345\n";
$result = xdiff_string_patch($str, $patch, XDIFF_PATCH_NORMAL, $error);
var_dump($result === $str);
var_dump($error === $patch);


Expected result:
----------------
bool(true)
bool(true)


Actual result:
--------------
bool(true)
bool(false)