Add work around for courses in weekly format with no end date to calculate from number of weeks

It was raised in MDL-58490 that in cases where the course format is set to weekly and no course end date is set that we could calculate the end date by the start date + number of weeks and use that to categorise into "in-progress" or "past" within the block.

MDL-56251 has already been raised to address this in core however it not as trivial of a problem as it may seem.

This issue is specifically to add a work around in the overview block while the actual problem is addressed in core.