Prevented RHS from closing when you reply to a message that had been deleted. (#5651)

webapp/components/create_comment.jsx

@@ -209,6 +209,8 @@ export default class CreateComment extends React.Component {
             (err) => {
                 if (err.id === 'api.post.create_post.root_id.app_error') {
                     this.showPostDeletedModal();
+                    PostStore.removePendingPost(post.channel_id, post.pending_post_id);
+                    this.setState({message: post.message});
                 } else {
                     this.forceUpdate();
                 }