try to disable payment info if total = 0

checkout.tpl

@@ -713,6 +713,16 @@
 				
             </div>
         </div>
+        {else}
+            <input type="hidden"
+                name="paymentmethod"
+                value="swiss_slip" 
+                data-payment-type="Invoices" 
+                data-show-local="false"
+                data-remote-inputs="false"
+                class="payment-methods"
+                checked
+            />
         {/if}
     </div>
 
@@ -1390,7 +1400,7 @@
                     <p class="small text-muted margin-bottom">{$LANG.orderForm.preferredPaymentMethod}</p>
                     {*
                     <div class="alert alert-success text-center large-text" role="alert" id="totalDueToday">
-			{$LANG.ordertotalduetoday}: &nbsp; <strong id="totalCartPrice">{$total}</strong>
+		            	{$LANG.ordertotalduetoday}: &nbsp; <strong id="totalCartPrice">{$total}</strong>
                     </div>
                     *}
 
@@ -1556,6 +1566,16 @@
                             </p>
                         {/if}
                     {/if}
+                {else}
+                    <input type="hidden"
+                        name="paymentmethod"
+                        value="swiss_slip" 
+                        data-payment-type="Invoices" 
+                        data-show-local="false"
+                        data-remote-inputs="false"
+                        class="payment-methods"
+                        checked
+                    />
                 {/if}
                     {if $shownotesfield}
                         <h4>{$LANG.orderForm.additionalNotes}</h4>