Fix wrong update with shadow catcher and transparent film

This change fixes an issue when scene has a shadow catcher and film is
configured to be transparent. Starting viewport render and making the
background non-transparent will cause bad memory access (wrong render
and possibly crash).

Film passes depends on transparency of background, so check for this.

Demo file: F10650585

Differential Revision: https://developer.blender.org/D12666

intern/cycles/render/film.cpp

@@ -434,7 +434,8 @@ void Film::update_passes(Scene *scene, bool add_sample_count_pass)
   const ObjectManager *object_manager = scene->object_manager;
   Integrator *integrator = scene->integrator;
 
-  if (!is_modified() && !object_manager->need_update() && !integrator->is_modified()) {
+  if (!is_modified() && !object_manager->need_update() && !integrator->is_modified() &&
+      !background->is_modified()) {
     return;
   }