resource: take a ref from iter to res only if res fully initialized

The sid_resource_iter_create normally takes a reference to the resource.
However, we cannot take the ref if we are creating the iterator inside
resource's 'create' callback in which case we're actually creating an
iterator that is internal to the resource,. Such iterator would need
to be destroyed in resource's 'destroy' callback (causing the resource
to be unreffed). We would never get to that because the 'destroy' callback
is called only after the ref_count hits 0.

Currently, the only resource API function that takes a ref is the
sid_resource_iter_create, but the same would apply for any other API
function that could be called inside resource's create callback.

src/resource/resource.c

@@ -69,6 +69,7 @@ typedef struct sid_resource_iter {
 	struct list *   prev; /* for safety */
 	struct list *   current;
 	struct list *   next; /* for safety */
+	bool            res_refd : 1;
 } sid_resource_iter_t;
 
 typedef enum
@@ -1110,7 +1111,10 @@ sid_resource_iter_t *sid_resource_iter_create(sid_resource_t *res)
 	if (!(iter = malloc(sizeof(*iter))))
 		return NULL;
 
-	iter->res = sid_resource_ref(res);
+	if ((iter->res_refd = res->initialized))
+		iter->res = sid_resource_ref(res);
+	else
+		iter->res = res;
 
 	iter->current = &res->children;
 	iter->prev    = iter->current->p;
@@ -1168,7 +1172,8 @@ void sid_resource_iter_reset(sid_resource_iter_t *iter)
 
 void sid_resource_iter_destroy(sid_resource_iter_t *iter)
 {
-	(void) sid_resource_unref(iter->res);
+	if (iter->res_refd)
+		(void) sid_resource_unref(iter->res);
 	free(iter);
 }