Fix errors notice in custom_breadcrumbs_theme_menu_item [#1795404]

In custom_breadcrumbs.module :

function custom_breadcrumbs_theme_menu_item($link, $has_children, $menu = '', $in_active_trail = FALSE, $extra_class = NULL) {
  ...

  /* When theme('menu_item') is called, the menu tree below it has been
   * rendered already. Since we are done on this recursion level,
   * one element must be popped off the stack.
   */

  $item = _custom_breadcrumbs_menu_stack();

  // If there are children, but they were not loaded...
  if ($has_children && !$menu) {
    // Load the tree below the current position.
    $tree = _custom_breadcrumbs_menu_subtree($item);

    ...
  }
<code>

But I have the case where $item can be empty and it results in NOTICE ERRORS. This can be easily fixed:

<code>
  // If there are children, but they were not loaded...
  if (!empty($item) && $has_children && !$menu) {
    ...