Depsgraph: Allow querying NULL IDs for evaluated version

Saves us from extra checks for NULL pointers when using datablocks for read.

source/blender/depsgraph/intern/depsgraph_query.cc

@@ -151,6 +151,9 @@ Object *DEG_get_evaluated_object(const Depsgraph *depsgraph, Object *object)
 
 ID *DEG_get_evaluated_id(const Depsgraph *depsgraph, ID *id)
 {
+	if (id == NULL) {
+		return NULL;
+	}
 	/* TODO(sergey): This is a duplicate of Depsgraph::get_cow_id(),
 	 * but here we never do assert, since we don't know nature of the
 	 * incoming ID datablock.