iterator: remove duplicate memset

When allocating new tree iterator frames, we zero out the allocated
memory twice. Remove one of the `memset` calls.

src/iterator.c

@@ -543,8 +543,6 @@ static int tree_iterator_frame_init(
 	new_frame = git_array_alloc(iter->frames);
 	GIT_ERROR_CHECK_ALLOC(new_frame);
 
-	memset(new_frame, 0, sizeof(tree_iterator_frame));
-
 	if ((error = git_tree_dup(&dup, tree)) < 0)
 		goto done;
 
@@ -558,8 +556,8 @@ static int tree_iterator_frame_init(
 	cmp = iterator__ignore_case(&iter->base) ?
 		tree_iterator_entry_sort_icase : NULL;
 
-	if ((error = git_vector_init(
-		&new_frame->entries, dup->entries.size, cmp)) < 0)
+	if ((error = git_vector_init(&new_frame->entries,
+				     dup->entries.size, cmp)) < 0)
 		goto done;
 
 	git_array_foreach(dup->entries, i, tree_entry) {