title: Redis subscriber is not notified by EXPIRE key 0
body: <p>I've got a Redis client subscribed to <code>__keyevent@0__:expired</code> notifications. It works perfectly, either when the key expires by itself (ttl reached) or when I expire them manually with a number of seconds greater than 0, like so:</p>
  
  <pre><code>EXPIRE myKey 1
  </code></pre>
  
  <p>The subscriber sees the <code>expired</code> event and can therefore take some actions.</p>
  
  <p>However, if I want to manually <strong>delete</strong> the key <strong>and</strong> have the subscriber notified, I use <code>EXPIRE</code> with 0 as the number of seconds:</p>
  
  <pre><code>EXPIRE myKey 0
  </code></pre>
  
  <p>The key gets deleted, but the subscriber doesn't receive anything.</p>
  
  <p>I can't see anything related to this in the doc. Can anyone explain this behavior?</p>