If the increment is 0 but this is a scroll axis, it's definitely a bug.
Nonetheless, it has happened, so put a warning in and a return statement
that we avoid the infinite loop and hopefully be able to reproduce later.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Keith Packard <keithp@keithp.com>