dix: don't allow disabling XTest devices

Disabling a XTest device followed by an XTest API call crashes the server.
This could be fixed elsewhere but disabled devices must not send events
anyway. The use-case for disabled XTest devices is somewhat limited, so
simply disallow disabling the devices.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Keith Packard <keithp@keithp.com>

Xi/chgdctl.c

@@ -187,7 +187,10 @@ ProcXChangeDeviceControl(ClientPtr client)
     case DEVICE_ENABLE:
         e = (xDeviceEnableCtl *) &stuff[1];
 
-        status = ChangeDeviceControl(client, dev, (xDeviceCtl *) e);
+        if (IsXTestDevice(dev, NULL))
+            status = !Success;
+        else
+            status = ChangeDeviceControl(client, dev, (xDeviceCtl *) e);
 
         if (status == Success) {
             if (e->enable)