Fix use of uninitialized memory in BKE_scene_objects_as_gset

Share macro for setting BLI_Iterator defaults to ensure
this doesn't happen again in cases the ITER_* macros aren't used.

Oversight in 14d74fb341.

source/blender/blenkernel/intern/collection.c

@@ -2033,8 +2033,9 @@ void BKE_scene_collections_iterator_begin(BLI_Iterator *iter, void *data_in)
   CollectionsIteratorData *data = MEM_callocN(sizeof(CollectionsIteratorData), __func__);
 
   data->scene = scene;
+
+  BLI_ITERATOR_INIT(iter);
   iter->data = data;
-  iter->valid = true;
 
   scene_collections_array(scene, (Collection ***)&data->array, &data->tot);
   BLI_assert(data->tot != 0);
@@ -2079,6 +2080,8 @@ typedef struct SceneObjectsIteratorData {
 static void scene_objects_iterator_begin(BLI_Iterator *iter, Scene *scene, GSet *visited_objects)
 {
   SceneObjectsIteratorData *data = MEM_callocN(sizeof(SceneObjectsIteratorData), __func__);
+
+  BLI_ITERATOR_INIT(iter);
   iter->data = data;
 
   /* Lookup list to make sure that each object is only processed once. */

source/blender/blenlib/BLI_iterator.h

@@ -34,13 +34,19 @@ typedef struct BLI_Iterator {
 typedef void (*IteratorCb)(BLI_Iterator *iter);
 typedef void (*IteratorBeginCb)(BLI_Iterator *iter, void *data_in);
 
+#define BLI_ITERATOR_INIT(iter) \
+  { \
+    (iter)->skip = false; \
+    (iter)->valid = true; \
+  } \
+  ((void)0)
+
 #define ITER_BEGIN(callback_begin, callback_next, callback_end, _data_in, _type, _instance) \
   { \
     _type _instance; \
     IteratorCb callback_end_func = callback_end; \
     BLI_Iterator iter_macro; \
-    iter_macro.skip = false; \
-    iter_macro.valid = true; \
+    BLI_ITERATOR_INIT(&iter_macro); \
     for (callback_begin(&iter_macro, (_data_in)); iter_macro.valid; callback_next(&iter_macro)) { \
       if (iter_macro.skip) { \
         iter_macro.skip = false; \

source/blender/makesrna/intern/rna_scene.c

@@ -778,7 +778,6 @@ static void rna_Scene_objects_begin(CollectionPropertyIterator *iter, PointerRNA
   Scene *scene = (Scene *)ptr->data;
   iter->internal.custom = MEM_callocN(sizeof(BLI_Iterator), __func__);
 
-  ((BLI_Iterator *)iter->internal.custom)->valid = true;
   BKE_scene_objects_iterator_begin(iter->internal.custom, (void *)scene);
   iter->valid = ((BLI_Iterator *)iter->internal.custom)->valid;
 }