Fix coasting for negative scroll directions
Fix coasting for negative scroll directions

1874094f0e99d8db319f6cf769ce5a25c9bc490c introduced negative scroll
directions. Coasting assumed always-positive increments and triggered an
endless scrolling loop.

Reported-by: Matthias Clasen <097d21dc5518307d71567a83214156cf1ca80f59@redhat.com>
Signed-off-by: Peter Hutterer <b9c50af7afa7642f6f854434cda9ffe54ece8b85@who-t.net>
Reviewed-by: Chase Douglas <69e02ec421aa70a149511825d897f2549ceee9a2@canonical.com>

Lyude/xf86-input-synaptics,mortehu/xf86-input-synaptics,quadpixels/three-finger-dragging,ssaavedra/xf86-input-synaptics,felipejfc/xserver-xorg-input-synaptics,eyko/xf86-input-synaptics,RsrchBoy/xserver-xorg-input-synaptics,mmonaco/xf86-input-synaptics,eyko/xf86-input-synaptics,sencer/synaptics,gdestuynder/xf86-input-synaptics,philipn/xserver-xorg-input-synaptics,mortehu/xf86-input-synaptics,mmonaco/xf86-input-synaptics,philipn/xserver-xorg-input-synaptics,corcoran/xserver-xorg-input-synaptics,ssaavedra/xf86-input-synaptics,Lyude/xf86-input-synaptics,gdestuynder/xf86-input-synaptics,corcoran/xserver-xorg-input-synaptics,sencer/synaptics,quadpixels/three-finger-dragging,RsrchBoy/xserver-xorg-input-synaptics,felipejfc/xserver-xorg-input-synaptics,jiixyj/xf86-input-synaptics,jiixyj/xf86-input-synaptics,nanderson94/xf86-input-synaptics,nanderson94/xf86-input-synaptics,felipejfc/xserver-xorg-input-synaptics,philipn/xserver-xorg-input-synaptics