Improve logging of rate-limited requests

The logging code was updated to handle anonymous customers differently
than authenticated ones when logging rate limit errors. For anonymous
requests, the obscured customer ID is replaced with the string
"anonymous" instead of attempting to obscure an empty email address.
This avoids exceptions and provides clearer logs when anonymous users
hit API limits.

lib/onetime/app/helpers.rb

@@ -60,7 +60,11 @@ def carefully redirect=nil
       secret_not_found_response
 
     rescue OT::LimitExceeded => ex
-      obscured = OT::Utils.obscure_email(cust.custid)
+      obscured = if cust.anonymous?
+                   'anonymous'
+                 else
+                   OT::Utils.obscure_email(cust.custid)
+                 end
       err "[limit-exceeded] #{obscured}(#{sess.ipaddress}): #{ex.event}(#{ex.count}) #{sess.identifier.shorten(10)}"
       err req.current_absolute_uri
       err ex.backtrace