Don't try to enable a NULL device
If there is no other libinput device in our list (and next is thus NULL), skip the xf86AddEnabledDevice() call.
Fixes #60 (closed) (second part, see !48 (merged) for the first part)
If there is no other libinput device in our list (and next is thus NULL), skip the xf86AddEnabledDevice() call.
Fixes #60 (closed) (second part, see !48 (merged) for the first part)