fix cdUp logic

[ysalmon]

Closes #731.

I did not change the assert(false) part although I do not really understand why it is here : Qt says that the logical operation of moving up is just not done if the parent directory does not exist, so even in the rare case of /.git, we could just keep running or display a warning.

[Murmele]

According to the documentation: This is the path of the .git folder for normal repositories, or of the repository itself for bare repositories.
https://libgit2.org/libgit2/#HEAD/group/repository/git_repository_path
So I don't understand why it could that the folder is not the .git folder?

[ysalmon]

We may have a repository that is bare in the sense that its worktree is not at the same place as its configuration directory, in which case the configuration directory is not ``repo/.git`` but just ``repo``. That's what I am addressing in my issue. -- Cordialement, Yann Salmon Depuis mon téléphone ; excusez la brièveté.

[Murmele]

Thanks for the clarification. I will merge it as soon as the ci build is working again