[clang-tools-extra] [clang-doc][fix] crashes when generating HTML without `--repository` (PR #131698)

[Paul Kirth via cfe-commits]

https://github.com/ilovepi requested changes to this pull request.

Thanks for the PR, but I don't think this is logic is quite right as it stands. There should also be some accompanying test changes to reflect what's being fixed. As this patch stands it removes basic functionality.

https://github.com/llvm/llvm-project/pull/131698