[mutter] clutter/pick-stack: Avoid uninitialized cairo_region_subtract_rectangle

[Marge Bot <marge-bot src gnome org>]

commit b2805dd5a6c22a102b7a59111bbde15a78861468
Author: Daniel van Vugt <daniel van vugt canonical com>
Date:   Tue Mar 29 18:08:27 2022 +0800

    clutter/pick-stack: Avoid uninitialized cairo_region_subtract_rectangle
    
    This fixes instances of:
    ```
    *** BUG ***
    In pixman_region32_init_rect: Invalid rectangle passed
    Set a breakpoint on '_pixman_log_error' to debug
    ```
    seen when navigating the overview and launching apps.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2349>

 clutter/clutter/clutter-pick-stack.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/clutter/clutter/clutter-pick-stack.c b/clutter/clutter/clutter-pick-stack.c
index db5c8d385d..e11d2489c0 100644
--- a/clutter/clutter/clutter-pick-stack.c
+++ b/clutter/clutter/clutter-pick-stack.c
@@ -491,7 +491,9 @@ calculate_clear_area (ClutterPickStack  *pick_stack,
           rec->base.rect.y1 == rec->base.rect.y2))
         continue;
 
-      clutter_actor_get_paint_box (rec->actor, &paint_box);
+      if (!clutter_actor_get_paint_box (rec->actor, &paint_box))
+        continue;
+
       cairo_region_subtract_rectangle (area,
                                        &(cairo_rectangle_int_t) {
                                          .x = paint_box.x1,