Unnecessary check in uc_product_forms()

Patch actually removes the useless first check causing the notice.

Bad formulation from me: the check is useless, the notice happens on an earlier version (6.x-2.2) where the unnecessary check was not yet wrapped in a isset() as it is now. It looked like this:

function uc_product_forms($form_id, $args) {
  $forms = array();
  if (is_object($args[0]) && isset($args[0]->type)) {

The notice happens on the $args[0] because $args is just array(), which does not have a 0 index, when invoked from drupal_retrieve_form() without additional args on the upstream drupal_get_form(), I guess.