Fix T85142: BMW scene quits Blender

Technically, the crash was caused by revert which happened in
rBcd24712c2c5: it reverted some code which is essential for
rB76fd41e9db1.

Bring back the essential code for the removal of un-needed
Copy-on-Write operations, so that the crash doesn't happen.

What was causing the crash is the ID tag assuming Copy-on-Write
operation always exists.

1 files changed, 4 insertions, 0 deletions

diff --git a/source/blender/depsgraph/intern/depsgraph_tag.cc b/source/blender/depsgraph/intern/depsgraph_tag.cc
index 95ee8234ef3..c60ec4351bc 100644
--- a/source/blender/depsgraph/intern/depsgraph_tag.cc
+++ b/source/blender/depsgraph/intern/depsgraph_tag.cc
@@ -265,6 +265,10 @@ void depsgraph_update_editors_tag(Main *bmain, Depsgraph *graph, ID *id)
 void depsgraph_id_tag_copy_on_write(Depsgraph *graph, IDNode *id_node, eUpdateSource update_source)
 {
   ComponentNode *cow_comp = id_node->find_component(NodeType::COPY_ON_WRITE);
+  if (cow_comp == nullptr) {
+    BLI_assert(!deg_copy_on_write_is_needed(GS(id_node->id_orig->name)));
+    return;
+  }
   cow_comp->tag_update(graph, update_source);
 }