backends: Only default to builtin panel on touchscreen devices

Non-display-attached tablets (e.g. Intuos) may find no match, which
should mean "use the span of all monitors", not "pick one for me".
Reserve this fallback to touchscreen devices, since these might
still benefit from it.

(cherry-picked from commit e3702c8b)

src/backends/meta-input-mapper.c

@@ -536,13 +536,17 @@ guess_candidates (MetaInputMapper     *mapper,
 
   if (info->matches->len == 0)
     {
-      DeviceMatch match = { 0 };
+      if (clutter_input_device_get_device_type (input->device) ==
+          CLUTTER_TOUCHSCREEN_DEVICE)
+        {
+          DeviceMatch match = { 0 };
 
-      match.monitor =
-        meta_monitor_manager_get_laptop_panel (mapper->monitor_manager);
+          match.monitor =
+            meta_monitor_manager_get_laptop_panel (mapper->monitor_manager);
 
-      if (match.monitor != NULL)
-        g_array_append_val (info->matches, match);
+          if (match.monitor != NULL)
+            g_array_append_val (info->matches, match);
+        }
 
       info->best = 0;
     }