Don't display draft restore prompt after a failed submit attempt (#52)

apps/map/templates/map/form.html

@@ -56,6 +56,8 @@
 
   <div class="savebutton"></div>
 
+  <input type="hidden" id="form_errors" value="{% if form.errors %}true{% else %}false{% endif %}">
+
   {% crispy form %}
 {% endblock %}
 
@@ -479,11 +481,15 @@ function showDraftPrompt(formSaver, serialisedForm) {
 }
 
 function initDrafts() {
-  var formSaver = new FormSaver({
+  const formSaver = new FormSaver({
     formId: 'case-study-form',
     except: [ 'csrfmiddlewaretoken' ]
   })
 
+  // Use whether the form has errors as a proxy for whether the server has
+  // returned us data in the form.  In this case, don't show a draft.
+  const formHasErrors = document.getElementById('form_errors').value === 'true' ? true : false
+  if (!formHasErrors) {
   // Get the previous draft, if any
     apiGetDraft()
       .then(response => response.json())
@@ -499,6 +505,7 @@ function initDrafts() {
       }).catch(err => {
         console.error(err);
       })
+  }
 
   // Init the button controller
   var button = new SaveButton(document.querySelector('.savebutton'))