Xi: initialize the device before applying button map changes.

This part got lost in bc909f7136.
Reported by Tomas Carnecky.

Acked-by: Daniel Stone <daniel@fooishbar.org>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

Xi/setbmap.c

@@ -101,6 +101,10 @@ ProcXSetDeviceButtonMapping(ClientPtr client)
 			  stuff->map_length + 3) >> 2)
 	return BadLength;
 
+    ret = dixLookupDevice(&dev, stuff->deviceid, client, DixManageAccess);
+    if (ret != Success)
+        return ret;
+
     rep.repType = X_Reply;
     rep.RepType = X_SetDeviceButtonMapping;
     rep.length = 0;