Don't throw in source_url() due to a non-existing source file

[mortenpi]

@clouds56: sorry it took me this long to get back to you on #1923, but I think this fix is more correct. relpath_from_repo_root and repo_commit are only called in edit_url and source_url, and they should never get called with a non-existing file. That source_url sometimes does was an oversight from #1808.

It might still be a good idea to add an isfile(file) || error("...") to those functions though, just to explicitly catch this case in the future, and you're welcome to update the PR with that.

This should fix the CI errors you reported, which I'm testing over at JuliaLang/julia#47105.

[fredrikekre]

WIll the fact that these are not found mean links will be broken in the julia docs?

[clouds56]

Thanks!

[mortenpi]

WIll the fact that these are not found mean links will be broken in the julia docs?

Yes, there are broken links, already now. In particular, the standard libraries are problematic, e.g. see anything in LinearAlgebra. That's next on my list to look into, but goes a bit out of scope of this one, which just aims to fix the regression where it now throws and kills Documenter.