submodule sync: Update "submodule.<name>.url" for empty directories

If a submodule directory has not been filled by "git submodule update"
yet, then "git submodule sync" must still update the super-project's
configuration for submodule.<name>.url.

This situation occurs when switching between branches with a module from
different urls and other branches without the submodule.
Signed-off-by: NAndreas Köhler <andi5.py@gmx.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -836,11 +836,12 @@ cmd_sync()
 			;;
 		esac
 
+		say "Synchronizing submodule url for '$name'"
+		git config submodule."$name".url "$url"
+
 		if test -e "$path"/.git
 		then
 		(
-			say "Synchronizing submodule url for '$name'"
-			git config submodule."$name".url "$url"
 			clear_local_git_env
 			cd "$path"
 			remote=$(get_default_remote)

t/t7403-submodule-sync.sh

@@ -23,7 +23,9 @@ test_expect_success setup '
 	 git commit -m "submodule"
 	) &&
 	git clone super super-clone &&
-	(cd super-clone && git submodule update --init)
+	(cd super-clone && git submodule update --init) &&
+	git clone super empty-clone &&
+	(cd empty-clone && git submodule init)
 '
 
 test_expect_success 'change submodule' '
@@ -64,4 +66,12 @@ test_expect_success '"git submodule sync" should update submodule URLs' '
 	)
 '
 
+test_expect_success '"git submodule sync" should update submodule URLs if not yet cloned' '
+	(cd empty-clone &&
+	 git pull &&
+	 git submodule sync &&
+	 test -d "$(git config submodule.submodule.url)"
+	)
+'
+
 test_done