When checking whether we are in a git repository or not, remove all symbolic
links in the current path before looking for a .git in the current path;
otherwise, symbolic links might mislead `locate-dominating-file` to find some
.git directory which is only reachable via symbolic links, which subsequently is
ignored by git (rightly so!) and thus yields errors.
Also, catch the case that the current git repository is not initialized yet by
checking the return value of `git rev-parse --abbrev-ref HEAD`.