[mutter] input-settings: treat a serial of 1 as serial of 0

[Carlos Garnacho <carlosg src gnome org>]

commit 9f3d321bf22335bf679c4d2640b4ea46da096d00
Author: Peter Hutterer <peter hutterer who-t net>
Date:   Mon Dec 17 15:22:44 2018 +1000

    input-settings: treat a serial of 1 as serial of 0
    
    The Wacom Xorg driver assigns a serial number of 1 for any pad that doesn't
    have a serial. libinput assigns 0. Just treat 1 as 0 here, there are no pens
    with a real serial 1 anyway.
    
    Fixes https://gitlab.gnome.org/GNOME/mutter/issues/414

 src/backends/meta-input-settings.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/src/backends/meta-input-settings.c b/src/backends/meta-input-settings.c
index 365577ec0..1d989f397 100644
--- a/src/backends/meta-input-settings.c
+++ b/src/backends/meta-input-settings.c
@@ -1326,7 +1326,9 @@ lookup_tool_settings (ClutterInputDeviceTool *tool,
 
   serial = clutter_input_device_tool_get_serial (tool);
 
-  if (serial == 0)
+  /* The Wacom driver uses serial 1 for serial-less devices but 1 is not a
+   * real serial, so let's custom-case this */
+  if (serial == 0 || serial == 1)
     {
       path = g_strdup_printf ("/org/gnome/desktop/peripherals/stylus/default-%s:%s/",
                               clutter_input_device_get_vendor_id (device),