Handle when git repo is fetched without history / no commits

[pi0]

When git repository is fetched without history, (by default actions/checkout does this), changelogen encounters an error as it expects at least one commit with error Cannot read properties of undefined (reading 'shortHash')

Example: https://github.com/unjs/ipx/actions/runs/6824241355/job/18559741909

Right solution is to set fetch-depth for action but i think changelogen should also handle this.