🐛 Fixed error when opening editor after abandoning a new tag

no issue

- the new tag that is added to the store when opening the new tag route was not being cleaned up when leaving the new tag route
- blank tags have a name value of `undefined` which causes errors when calling `localeCompare()` on them as is done when ordering tag names for display in the tags input

ghost/admin/app/routes/tags/new.js

@@ -15,7 +15,10 @@ export default AuthenticatedRoute.extend({
     // reset the model so that mobile screens react to an empty selectedTag
     deactivate() {
         this._super(...arguments);
-        this.set('controller.model', null);
+
+        let {controller} = this;
+        controller.model.rollbackAttributes();
+        controller.set('model', null);
     }
 
 });