Description:
------------
If a DateInterval is created using date_diff, the public attributes of the interval object return true on an empty check. However, if the object is called elsewhere first (for example, in a var_dump() or json_encode()) the attributes can be tested with empty().

Tested on 5.3.3 and 5.5.9-ubuntu.

Test script:
---------------
<?php
$date = new DateTime('2014-08-25');
$today = new DateTime('2014-08-29');
$interval = date_diff($date, $today);

// json_encode($interval);

if (!empty($interval->days)) {
	echo $interval->days;
} else if (!empty($interval->h)) {
	echo $interval->h;
} else {
	echo 'No matches';
}

Expected result:
----------------
4

Actual result:
--------------
string: 'No matches'