Fix an uninitialized variable

"has_discrete" gets set to true in if/else if, but gets left unset otherwise.
So let's initialize it to false.

(This was caught by valgrind.)

Signed-off-by: Dima Ryazanov <dima@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

libweston/compositor-wayland.c

@@ -1707,6 +1707,7 @@ input_handle_axis(void *data, struct wl_pointer *pointer,
 
 	weston_event.axis = axis;
 	weston_event.value = wl_fixed_to_double(value);
+	weston_event.has_discrete = false;
 
 	if (axis == WL_POINTER_AXIS_VERTICAL_SCROLL &&
 	    input->vert.has_discrete) {