object: fix struct zero-initialisation on MSVC

object-test/trees.c

@@ -66,8 +66,8 @@ int main(void)
 		printf("%u\n", item->value);
 	}
 
-	b_btree btree = {};
-	struct btree_item items3[NITEMS] = {};
+	b_btree btree = {0};
+	struct btree_item items3[NITEMS] = {0};
 	for (int i = 0; i < NITEMS; i++) {
 		items3[i].value = i;
 		put_node(&btree, &items3[i]);