gdbus: Fix crash when calling g_dbus_add_service_watch

If g_dbus_add_service_watch is called for service which bus name is
already known the following crash can happen:

invalid read of size 1
  at 0x4C2A2F2: strlen (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
  by 0x4E97722: g_strdup (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x405B0C: update_name_cache (watch.c:435)
  by 0x405C37: update_service (watch.c:593)
  by 0x4E7A2A5: g_main_context_dispatch (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4E7A627: ??? (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4E7AA39: g_main_loop_run (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4038EA: client_ready (test-gdbus-client.c:1014)
  by 0x4E9E5E0: ??? (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4E9E7A5: ??? (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4E9EB1A: g_test_run_suite (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x403614: main (test-gdbus-client.c:1058)
Address 0x5dbe5d0 is 0 bytes inside a block of size 7 free'd
  at 0x4C28577: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
  by 0x4E7FF7E: g_free (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x405B04: update_name_cache (watch.c:434)
  by 0x405C37: update_service (watch.c:593)
  by 0x4E7A2A5: g_main_context_dispatch (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4E7A627: ??? (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4E7AA39: g_main_loop_run (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4038EA: client_ready (test-gdbus-client.c:1014)
  by 0x4E9E5E0: ??? (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4E9E7A5: ??? (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x4E9EB1A: g_test_run_suite (in /usr/lib64/libglib-2.0.so.0.3800.2)
  by 0x403614: main (test-gdbus-client.c:1058)

gdbus/watch.c

@@ -595,7 +595,6 @@ static gboolean update_service(void *user_data)
 	struct filter_callback *cb = data->callback;
 	DBusConnection *conn;
 
-	update_name_cache(data->name, data->owner);
 	conn = dbus_connection_ref(data->conn);
 	service_data_free(data);