machinectl: fix printing of multiple addresses

We'd print everything jumbled together:
$ machinectl --max-addresses=3
MACHINE CLASS     SERVICE        OS     VERSION ADDRESSES
rawhide container systemd-nspawn fedora 30      169.254.40.164fe80::94aa:3aff:fe7b:d4b9

src/machine/machinectl.c

@@ -331,7 +331,7 @@ static int list_machines(int argc, char *argv[], void *userdata) {
                                 name,
                                 0,
                                 "",
-                                "",
+                                " ",
                                 arg_addrs,
                                 &addresses);