core: hhvm fix: GetCutOffDate in utils.php
core: hhvm fix: GetCutOffDate in utils.php

(hhvm/hack complains with the isset)

Signed-off-by: Etienne CHAMPETIER <d24370f93c848f9b9e9043ebb082d433901eaa60@fiducial.net>

RavenB/Z-Push-contrib,Freeaqingme/Z-Push-contrib,mta59066/Z-Push-contrib,fmbiete/Z-Push-contrib