Update scraper to handle rows without CRNs
We expect PatriotWeb to list the CRN for every time slot for a class, but it instead will occasionally skip details in common with the previous row which throws off the parser. It's unlikely that we will get this behavior corrected in PatriotWeb, so the scraper should be updated to handle this.
CC: @ahasan21 for reporting the issue
CC: @zwood2 for his investigation