Target git-import adds everything it finds in the current directory. If
it's already a Git project, that fails over git commit -m "First commit".
Since it's a prerequisite of target git-init-remote, it breaks that target,
too for non-empty git repos, which isn't helpful when trying to run make
git-init-remote to publish an an already existing project.
So only do something meaningful in git-import if the project it's run in
doesn't already contain files.
Signed-off-by: Jan Lindemann <jan@janware.com>