xfree86: Sanity check before retrieving the paired device.

Some pointer devices send key events [1], blindly getting the paired device
crashes the server. So let's check if the device is a pointer before we try to
get the paired device.

[1] The MS Wireless Optical Desktop 2000's multimedia keys are sent through
the pointer device, not through the keyboard device.

hw/xfree86/common/xf86Xinput.c

@@ -722,7 +722,10 @@ xf86PostKeyboardEvent(DeviceIntPtr      device,
     int index;
 
 #if XFreeXDGA
-    DeviceIntPtr pointer = GetPairedDevice(device);
+    DeviceIntPtr pointer;
+
+    /* Some pointers send key events, paired device is wrong then. */
+    pointer = IsPointerDevice(device) ? device : GetPairedDevice(device);
 
     if (miPointerGetScreen(pointer)) {
         index = miPointerGetScreen(pointer)->myNum;