pointer speed at -1 in flat profile gives us a factor of 0 and disables all mouse movement. That shouldn't happen.
commit d92d8554c3414f7bf136e2f9710426f46ad80a7a (HEAD -> master, tmp-today/master, origin/master)
Author: Peter Hutterer <firstname.lastname@example.org>
Date: Mon Sep 4 15:10:58 2017 +1000
filter: don't allow an accel factor of 0 on the flat profile