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).