webui: invalid commit links in default repository commits history page #1683

Context

When launching git bug web-ui, commit hyperlinks are broken in repository commits history. Each link lack _ component in URL for default-repository.

This bug was found on git-bug v0.11.0 d1819bd1dbd6 and is also present on d57831d4b94a.
It is caused by CommitRow component giving out /commit/$ref instead of /$repo/commit/$ref if repo is null.

Solution to consider

Default repo prop to _ in CommitRow component.

I will provide a PR with a straight-forward fix.
Note that I could not figure out when $repo is used in the webui, I am probably lacking a deeper understanding of the project.