dix: Guard against non-existing PtrFeedbackPtr

Trying to change the pointer control settings on a device without
PtrFeedbackPtr would be a bug and a crash in the Xserver.

Guard against that case by returning early with a BadImplementation
error, that might kill the X11 client but the Xserver would survive.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Related: xorg/xserver#1137
(cherry picked from commit dee2bb03)
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