- For a situation where `authored = 3`, `committed = 4`, the previous
calculation was `3 - 4` which meant that `committed = -1` in the end.
- This was incorrect, since a user can't have negative contributions!
- Instead, only do the subtraction to get the deduplicated `committed`
count if the number of authored commits is higher than the number of
committed commits. This approach should achieve the desired "don't
double count things that the user authored and committed, but do count
things that another person authored that the user committed".
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