Fix license argument test

src/stub

@@ -660,7 +660,7 @@ main() {
         *)        usage ;;
     esac
     updating && init_from_existing
-    if test -n $License; then
+    if test -n "$License"; then
         known_licenses | grep -qxF "$License" \
          || die "unknown license (use -L to get list): $License"
         MkLicense=true