inspector: Avoid an array overrun

Commit 3f56af3738 added a new value to the
GdkInputSource enum, forgetting that the inspector
has an array of names to match this enum.

Fixes: https://gitlab.gnome.org/GNOME/gtk/issues/2385

gtk/inspector/general.c

@@ -511,7 +511,8 @@ add_device (GtkInspectorGeneral *gen,
     "Keyboard",
     "Touchscreen",
     "Touchpad",
-    "Trackpoint"
+    "Trackpoint",
+    "Pad"
   };
 
   name = gdk_device_get_name (device);