Description:
------------
Datetime diff overflows if fractions and no fractions in same second.

Test script:
---------------
$date = new \DateTime('2018-11-08 10:22:43');
$date2 = new \DateTime('2018-11-08 10:22:43.123456');


print_r($date2->diff($date));


Expected result:
----------------
DateInterval Object
(
    [y] => 0
    [m] => 0
    [d] => 0
    [h] => 0
    [i] => 0
    [s] => 0
    [f] => -0.123456
    [weekday] => 0
    [weekday_behavior] => 0
    [first_last_day_of] => 0
    [invert] => 0
    [days] => 0
    [special_type] => 0
    [special_amount] => 0
    [have_weekday_relative] => 0
    [have_special_relative] => 0
)

Actual result:
--------------
DateInterval Object
(
    [y] => -1
    [m] => 11
    [d] => 30
    [h] => 23
    [i] => 59
    [s] => 59
    [f] => 0.876544
    [weekday] => 0
    [weekday_behavior] => 0
    [first_last_day_of] => 0
    [invert] => 0
    [days] => 0
    [special_type] => 0
    [special_amount] => 0
    [have_weekday_relative] => 0
    [have_special_relative] => 0
)