iterate resolve_badmsg(): fix retries when forwarding
This function just caused immediate SERVFAIL in FORWARD mode. If we get a bad message (various RCODEs, failed parse, etc.), we surely want to try other IP addresses even in forwarding modes. For SERVFAIL and REFUSED this regressed in e460f921 (since v5.1.0); for others it probably didn't work that way until now. Behavior for these two RCODEs in STUB mode remains an exception for now, as it's been there since forever (aecffe74).