Avoid outputing the coverage percent as -NaN%

If the sum of hits and miss are 0, the percent gets calculated as

    hits / (hits + miss) * 100

Normally this works fine, but if you're just starting a project, you'll get `0/0` which evaluates to `-nan`.  This fixes that by checking if `hits + miss` is `0` and then use `1` so we get `0/1` which evaluates to `0`.