ui: don't send any event if delta_y == 0

When the user raises their fingers from the touchpad, we may receive a
GDK_SMOOTH_SCROLL event with delta_y == 0. Avoid generating a WHEEL_UP
event in this situation.

Signed-off-by: Sergio Lopez <slp@redhat.com>
Message-id: 20190204122043.43007-1-slp@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

ui/gtk.c

@@ -1004,7 +1004,9 @@ static gboolean gd_scroll_event(GtkWidget *widget, GdkEventScroll *scroll,
                                          &delta_x, &delta_y)) {
             return TRUE;
         }
-        if (delta_y > 0) {
+        if (delta_y == 0) {
+            return TRUE;
+        } else if (delta_y > 0) {
             btn = INPUT_BUTTON_WHEEL_DOWN;
         } else {
             btn = INPUT_BUTTON_WHEEL_UP;