Make sure EDIT dialog for block fields always operates on up-to-date data.

To achieve this, remove TinyMCE from block fields on "Save" and
"Cancel" (previous version of the code was delaying this step until user
requested an EDIT dialog for another block).

xblockutils/public/studio_edit.js

@@ -14,6 +14,7 @@ function StudioEditableXBlockMixin(runtime, element) {
         fields.push({
             name: $wrapper.data('field-name'),
             isSet: function() { return $wrapper.hasClass('is-set'); },
+            hasEditor: function() { return tinyMceAvailable && $field.tinymce(); },
             val: function() {
                 var val = $field.val();
                 // Cast values to the appropriate type so that we send nice clean JSON over the wire:
@@ -31,6 +32,9 @@ function StudioEditableXBlockMixin(runtime, element) {
                         val = JSON.parse(val); // TODO: handle parse errors
                 }
                 return val;
+            },
+            removeEditor: function() {
+                $field.tinymce().remove();
             }
         });
         var fieldChanged = function() {
@@ -45,8 +49,6 @@ function StudioEditableXBlockMixin(runtime, element) {
             $resetButton.removeClass('active').addClass('inactive');
         });
         if (type == 'html' && tinyMceAvailable) {
-            if ($field.tinymce())
-                $field.tinymce().remove(); // Stale instance from a previous dialog. Delete it to avoid interference.
             tinyMCE.baseURL = baseUrl + "/js/vendor/tinymce/js/tinymce";
             $field.tinymce({
                 theme: 'modern',
@@ -82,6 +84,7 @@ function StudioEditableXBlockMixin(runtime, element) {
         fields.push({
             name: $wrapper.data('field-name'),
             isSet: function() { return $wrapper.hasClass('is-set'); },
+            hasEditor: function() { return false; },
             val: function() {
                 var val = [];
                 $checkboxes.each(function() {
@@ -146,11 +149,24 @@ function StudioEditableXBlockMixin(runtime, element) {
             } else {
                 notSet.push(field.name);
             }
+            // Remove TinyMCE instances to make sure jQuery does not try to access stale instances
+            // when loading editor for another block:
+            if (field.hasEditor()) {
+                field.removeEditor();
+            }
         }
         studio_submit({values: values, defaults: notSet});
     });
 
     $(element).find('.cancel-button').bind('click', function(e) {
+        // Remove TinyMCE instances to make sure jQuery does not try to access stale instances
+        // when loading editor for another block:
+        for (var i in fields) {
+            var field = fields[i];
+            if (field.hasEditor()) {
+                field.removeEditor();
+            }
+        }
         e.preventDefault();
         runtime.notify('cancel', {});
     });