Fix handling of server exceptions.

If we've raised an exception in on_headers or on_body we don't want to
continue processing this request. We've already sent the reply back, we're
essentially processing a failed request at this point.

Check if we have terminated the request and skip processing if so.

lib/goliath/connection.rb

@@ -56,7 +56,7 @@ def post_init
           @pending.push(req)
         end
 
-        req.process if !@parser.upgrade?
+        req.process if !@parser.upgrade? && !req.env[:terminate_connection]
       end
     end