Add an error message to the if statement if it fails.

sandbox/lua/decoders/bind_query_log.lua

@@ -101,7 +101,8 @@ function process_message ()
   fields = grammar:match(query_log_line)
 
   --If fields is empty, exit immediately:
-  if not fields then return -1 end
+  if not ok then return -1, "Failed to parse the BIND query log line." end
+
   --Set the time in the message we're generating and set it to nil in the original log line:
   msg.Timestamp = fields.time
   fields.time = nil