title: in_array function returns true when passing empty array
body: <p>I noticed the following strange occurrence:</p>
  
  <pre><code>var_dump(in_array("test", array_keys(array("hello"))));
  </code></pre>
  
  <p>Yields: <code>bool(true)</code></p>
  
  <p>How is this possible? Array does not contains keys, therefore <code>array_keys()</code> will return an empty array. Test is not in this empty array, so why would it return true? Is this a bug in PHP?</p>