Fix Panic When Cleaning Sum of Best

[CryZe]

When cleaning the sum of best, the message tries to be as helpful as possible by showing as much information about the problematic segments as possible. Part of that is information about the date of the attempt. However, as it turns out, the attempt may not actually exist. This shouldn't generally happen, but we can't trust the correctness of the splits files, so for whatever reason, the attempt may be missing. In that case, we simply skip that information.