title: myth-auth bug when integrated with codeigniter
body: <p>So, it seems like there is a bug in myth-auth when integrated with codeigniter.</p>
  <p>It tries to authenticate the <code>$password</code> even when the  <code>$email</code> is null.Therefore throwing the <code>Undefined offset: 1</code> exception.</p>
  <p>Here in <code>APPPATH\ThirdParty\myth-auth\src\Authentication\Passwords\NothingPersonalValidator.php</code> on line 91</p>
  <pre><code>84         // Use the pieces as needles and haystacks and look every which way for matches.
  85         if($valid)
  86         {
  87             // Take username apart for use as search needles
  88             $needles = $this-&gt;strip_explode($userName);
  89 
  90             // extract local-part and domain parts from email as separate needles
  91****             [$localPart, $domain] = \explode('@', $email);
  92             // might be john.doe@example.com and we want all the needles we can get
  93             $emailParts = $this-&gt;strip_explode($localPart);
  94             if( ! empty($domain))
  95             {
  96                 $emailParts[] = $domain;
  97             }
  98             $needles = \array_merge($needles, $emailParts);
  </code></pre>
  <p>That exception is always thrown whenever the email field is left empty, rather than it redirecting back with the</p>
  <blockquote>
  <p>'Email is left empty'</p>
  </blockquote>
  <p>error message</p>