check shoppingcard for free products

checkout.tpl

@@ -1636,6 +1636,8 @@
                         <button type="submit"
                                 id="btnCompleteOrder"
                                 class="margin-bottom btn btn-primary btn-lg disable-on-click spinner-on-click{if $captcha}{$captcha->getButtonClass($captchaForm)}{/if}"
+                                {if ((count($clientActiveFree) + count($clientCardFree)) > 1)}disabled="disabled"{/if}
+
                                 {if $cartitems==0}disabled="disabled"{/if}
                                 >
                                 {if $rawtotal==0}Kostenlos bestellen