Only show GST line if non-zero

pinaxcon/templates/registrasion/_invoice_details.html

@@ -46,10 +46,12 @@
 
     <tr><th colspan="4"></th></tr>
 
-    <tr>
-      <th colspan="3">Includes 10% Australian Goods and Services Tax</th>
-      <td class="text-right">${{ invoice.value|gst}}</td>
-    </tr>
+    {% if invoice.value|gst %}
+      <tr>
+        <th colspan="3">Includes 10% Australian Goods and Services Tax</th>
+        <td class="text-right">${{ invoice.value|gst}}</td>
+      </tr>
+    {% endif %}
 
     <tr>
       <th colspan="3">Total</th>