Set all valuators for relative motion events (#24737)

We should process all the deltas reported by a relative motion device,
otherwise some devices such as A4Tech X-750F or similar may trigger a
situation when the `v` array contains random values (it isn't
initialized anywhere) and later we process them and in effect the mouse
cursor "jumps" on the screen.
I'm not sure why, but we also must be sure that the `first` and `last`
variables reflect the axis map, otherwise the mouse cursor "jumps" on
the screen when clicking mouse buttons in some rare cases reported by
Bartek Iwaniec on Bugzilla. That's why a simple initialization of the
`v` array with zeros isn't sufficient.

X.Org Bug 24737 <http://bugs.freedesktop.org/show_bug.cgi?id=24737>

Signed-off-by: Bartosz Brachaczek <b.brachaczek@gmail.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit c1f16a4f59)

src/evdev.c

@@ -440,7 +440,7 @@ EvdevProcessValuators(InputInfoPtr pInfo, int v[MAX_VALUATORS], int *num_v,
         for (i = 0; i < REL_CNT; i++)
         {
             int map = pEvdev->axis_map[i];
-            if (pEvdev->delta[i] && map != -1)
+            if (map != -1)
             {
                 v[map] = pEvdev->delta[i];
                 if (map < first)