mod_sasl2_fast: Improve handling when SASL profile unexpectedly lacks CB
This fixes a traceback reported by riau, but likely does not solve the
underlying cause, whatever that is.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Reset password</title>
<link rel="stylesheet" href="bootstrap.min.css">
</head>
<body>
<div class="container">
<h1>Reset password</h1>
<div class="alert {classes}">{message}</div>
</div>
</body>
</html>