fix: check git status before using git version tag

[linonetwo]

This fixes the problem described in #1112

Otherwise, it will display version likes v0.33.0

[gklyne]

That certainly seems to be the cause of the problem.

But I worry where this "fix" is going if git describe behaves differently on different systems (which criticism applies also to my previous fix). It feels like a lurking problem waiting to bite.

An online search wasn't massively helpful, but did turn up:

• https://stackoverflow.com/questions/2180270/check-if-current-directory-is-a-git-repository
• https://stackoverflow.com/questions/2044574/determine-if-directory-is-under-git-control

On my system, git rev-parse exits silently with status 0 in a got repo, or with "fatal: Not a git repository (or any of the parent directories): .git" and status 128 if not. There seems to be a little consensus behind appropriate git rev-parse in this way - I guess because it dosn't actually do much with the repo itself?

[kjetilk]

LGTM

[linonetwo]

@gklyne I thought it is fine, because many people on Windows will install "Git for Windows", which behaves just like in Linux. And I tested it in MacOS, it is the same as Linux. So it might be a good enough solution.