Handle invalid post ids in editor route

No issue
-fail fast if an invalid post id is passed into the
 editor route to prevent an unnecessary network request
 for all posts
-if post id is valid but post does not exist, transition
 to Content screen instead of returning an invalid model

core/client/routes/editor.js

@@ -5,16 +5,32 @@ var EditorRoute = AuthenticatedRoute.extend(styleBody, {
     classNames: ['editor'],
 
     model: function (params) {
-        var post = this.store.getById('post', params.post_id);
+        var self = this,
+            post,
+            postId;
+
+        postId = Number(params.post_id);
+
+        if (!Number.isInteger(postId) || !Number.isFinite(postId) || postId <= 0) {
+            this.transitionTo('posts.index');
+        }
+
+        post = this.store.getById('post', postId);
 
         if (post) {
             return post;
         }
 
         return this.store.filter('post', { status: 'all', staticPages: 'all' }, function (post) {
-            return post.get('id') === params.post_id;
+            return post.get('id') === postId;
         }).then(function (records) {
-            return records.get('firstObject');
+            var post = records.get('firstObject');
+
+            if (post) {
+                return post;
+            }
+
+            return self.transitionTo('posts.index');
         });
     }
 });