resend_password_processing.php: do not throw on no email (#1974)

When the `email` request field doesn't exist, an error is thrown and it
sends a bug report email. Even though the actual page has an HTML5 form
property that prevents submitting an empty email, it appears that
crawlers are submitting this page without the `email` field.

We can prevent this bug report email if we default `email` to an empty
string, so that the user gets an error message response. This is not
ideal, because it means that if the form breaks (e.g. field is changed
without updating the processor), we won't get bug emails, but I think
this is necessary to avoid the sheer volume of crawler bug emails.

src/htdocs/resend_password_processing.php

@@ -7,7 +7,7 @@
 try {
 	require_once('../bootstrap.php');
 
-	$email = Request::get('email');
+	$email = Request::get('email', ''); // default prevents crawler bug report spam
 	if ($email === '') {
 		create_error('You must specify an e-mail address!');
 	}