Fixed two date display bugs in the Calendar Event details screen.
Both are cosmetic, the editing interface is not affected and is saving correctly.
1. Times between 12-1pm (ie. 1200-1259hrs) would show as, eg. "12:30 am" instead of "12:30 pm". (Squizmap #3979.)
   .. The JS code was assigning PM based on hours > 12 instead of hours >= 12.
2. Times between 12-1am (ie. 0000-0059hrs) would show as, eg. "00:30 am" instead of "12:30 am". (Squizmap #3980.)
   .. The JS code was not handling the case for hours = 0 properly.