Allow for a blocked period to be offered on different days when the option in Portal Options are set to "Take Attendance for Each Period in a Blocked Section".

For example, Period 4 has a 2 period block. Period 4 is offered on Monday. Period 5 is offered on Tuesday. Currently, when set up this way, the drop-down for Period 5 will show as a blank in the period dropdown for teacher attendance when it's not being offered that day. Only display the period offered according to the Calendar.