Backport of this commit:

  commit 7ba7085b4f01f3cd72008712a5333ea3f0edfd88
  Author: walter harms <wharms@bfs.de>
  Date:   Sat Oct 28 19:14:22 2017 +0200

    AuRead.c: remove redundant null check on calling free()

    this removes simply unneeded code from XauReadAuth
Signed-off-by: Walter Harms <wharms@bfs.de>
Reviewed-by: Daniel Martin <consume.noise@gmail.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>