wayland: Pass the inverted flag for horizontal scroll events

Natural scrolling affects both axes, and the compositor may not send the vertical axis orientation if the frame has no vertical scroll motion, so purely horizontal events need to be flagged as inverted as well.

src/video/wayland/SDL_waylandevents.c

@@ -1207,9 +1207,7 @@ static void pointer_handle_axis_relative_direction(void *data, struct wl_pointer
                                                    uint32_t axis, uint32_t axis_relative_direction)
 {
     SDL_WaylandSeat *seat = data;
-    if (axis != WL_POINTER_AXIS_VERTICAL_SCROLL) {
-        return;
-    }
+
     switch (axis_relative_direction) {
     case WL_POINTER_AXIS_RELATIVE_DIRECTION_IDENTICAL:
         seat->pointer.pending_frame.axis.direction = SDL_MOUSEWHEEL_NORMAL;