Backported from X.org:

   commit 512bac25ec0e980968b93a2ebe88bd89bf99b697
   Author: Daniel Stone <daniel@fooishbar.org>
   Date:   Tue Nov 6 14:52:03 2007 +0000

    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.
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>