xwm: Don't change focus on focus events from grabs

xwm would not let X clients change the focus behind the compositor's
back, reverting focus where it's supposed to be when this occurs.

However, X11 grab also issue focus in events, on which some clients
rely and reverting focus in this case braks the client logic (e.g.
combobox menu in gtk+ using the X11 backend).

Check if the focus event is actually coming from a grab or ungrab and
do not revert focus in this case, to avoid breaking clients logic.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Tested-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Acked-by: Daniel Stone <daniels@collabora.com>
Acked-by: Quentin Glidic <sardemff7+git@sardemff7.net>

xwayland/window-manager.c

@@ -2055,6 +2055,12 @@ static void
 weston_wm_handle_focus_in(struct weston_wm *wm, xcb_generic_event_t *event)
 {
 	xcb_focus_in_event_t *focus = (xcb_focus_in_event_t *) event;
+
+	/* Do not interfere with grabs */
+	if (focus->mode == XCB_NOTIFY_MODE_GRAB ||
+	    focus->mode == XCB_NOTIFY_MODE_UNGRAB)
+		return;
+
 	/* Do not let X clients change the focus behind the compositor's
 	 * back. Reset the focus to the old one if it changed. */
 	if (!wm->focus_window || focus->event != wm->focus_window->id)