Prevent NaN% widths for blank runs

[glacials]

Other than for testing I'm not sure why you'd upload a blank run, but if you do we end up dividing by 0 all over the place which means we get bars with NaN% widths.

I guess the most sane way to display the splits timeline would be to give each split an equal amount of space by using widths of 100/num_splits%. Obviously this isn't technically accurate, but the only accurate way to handle this would be to blow up. So it'll have to do.