Description:
------------
When using JSON_THROW_ON_ERROR, json_last_error no longer refers to the previous function call, but instead the last json_(encode|decode) that doesn't have the JSON_THROW_ON_ERROR flag set.

Test script:
---------------
$foo = json_decode('[bar');


// many lines of code.
$bar = json_encode('Hello world!', JSON_THROW_ON_ERROR);
if (json_last_error() !== JSON_ERROR_NONE) {
    // Note, this is not true. The encoding was fine, but
    // json_last_error gets the error from the json_decode before
    throw new Exception("encoding went wrong!");
}

echo "All is fine";



Expected result:
----------------
json_last_error() gives the error for the last call, regardless of the flag.

Actual result:
--------------
json_last_error() give the error for the previous that did not have JSON_THROW_ON_ERROR set.