topdir.mk: Make target git-import idempotent

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>

make/topdir.mk

@@ -224,9 +224,12 @@ git-clone-to-remote:
 	make git-update-project-description
 
 git-import: git-init git-config
-	git add -A
+	if ! git ls-files | grep -q .; then \
-	git status
+		set -ex ;\
-	git commit -am "First commit"
+		git add -A ;\
+		git status ;\
+		git commit -am "First commit" ;\
+	fi
 
 git-init-remote: git-import git-clone-to-remote