[PATCH] Some undefined offsets

With WP_DEBUG on I’m getting a few warnings on the widgets list page. In /plugins/contextual-related-posts/contextual-related-posts.php:307
change

$title = esc_attr($instance['title']);
$limit = esc_attr($instance['limit']);
$show_excerpt = esc_attr($instance['show_excerpt']);
$post_thumb_op = esc_attr($instance['post_thumb_op']);
$thumb_height = esc_attr($instance['thumb_height']);
$thumb_width = esc_attr($instance['thumb_width']);

to

$title = isset($instance['title']) ? esc_attr($instance['title']) : '';
$limit = isset($instance['limit']) ? esc_attr($instance['limit']) : '';
$show_excerpt = isset($instance['show_excerpt']) ? esc_attr($instance['show_excerpt']) : '';
$post_thumb_op = isset($instance['post_thumb_op']) ? esc_attr($instance['post_thumb_op']) : '';
$thumb_height = isset($instance['thumb_height']) ? esc_attr($instance['thumb_height']) : '';
$thumb_width = isset($instance['thumb_width']) ? esc_attr($instance['thumb_width']) : '';

http://ww.wp.xz.cn/plugins/contextual-related-posts/