Fixing bug where 12pm becomes 24pm

Now if a user sends a voice action 'Dismiss alarm for 12pm' we (mistakenly)
convert that to HOUR_OF_DAY = 24 instead of HOUR_OF_DAY = 12.
This CL changes it so that +12 hours is added only if hour < 12.

Change-Id: I5b505a6eb5c154cca49f1f37bde7f21f8081948d