DIX: XKB: Set xkbInfo to NULL as well as freeing it (bug #10639)

XkbRemoveResourceClient wants to access xkbInfo if it exists, so make
sure we NULL it after freeing it.  It doesn't make much sense to move
the RemoveResourceClient call first, as there's not much point in
notifying clients while we're shutting the server down anyway.

dix/devices.c

@@ -528,6 +528,7 @@ CloseDevice(DeviceIntPtr dev)
 	if (dev->key->xkbInfo)
 	    XkbFreeInfo(dev->key->xkbInfo);
 #endif
+        dev->key->xkbInfo = NULL;
 	xfree(dev->key->curKeySyms.map);
 	xfree(dev->key->modifierKeyMap);
 	xfree(dev->key);