shell_dbus_acquire_name: Don't leak error

If fatal is not set, we return from this function in the error
case. Don't leak the GError if that happens.

src/main.c

@@ -69,6 +69,7 @@ shell_dbus_acquire_name (GDBusProxy  *bus,
                                                        &error)))
     {
       g_printerr ("failed to acquire %s: %s\n", name, error->message);
+      g_clear_error (&error);
       if (!fatal)
         return;
       exit (1);