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.
You can reproduce this issue with CRN 20921. Searching it on Schedules will show only the Tuesday class. Searching it on PatriotWeb will return:
CC: @ahasan21 for reporting the issue
CC: @zwood2 for his investigation
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