Fix calculation of next DateChangedEvent time

Calendar.HOUR indicates the hour of the morning or afternoon. In the
morning this is no problem, but if this method is called after noon, it
will schedule the alarm for 12:00 the next day instead of 00:00.

Change-Id: Ibce239a6c7a41df85cf0c6ca3f45871a581eb7d9
Frameworks: Lockscreen background - 1/2