commit f7652afa upstream.

A malicious caller could otherwise hand over handles to other objects
causing all sorts of interesting problems.

Testing done: Ran a Fedora 25 desktop using both Xorg and
gnome-shell/Wayland.
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>