Condition to check previous next article post title

Try to use get_next_post() to check if next post exists

if(strlen(get_next_post()->post_title) > 0)
{
    //show your next post link
}

Try to use get_previous_post() to check if previous post exists

if(strlen(get_previous_post()->post_title) > 0)
{
    //show your previous post link
}