Assorted fixes

* Fix #679 (borked reply to `JOIN #chan,\r\n`)
* Replace invalid error parameters with *'s in various places
* Fix PART with no message sending an empty trailing parameter to the channel
* Fix some error responses not getting labeled

irc/utils/args.go

@@ -54,3 +54,12 @@ func StringToBool(str string) (result bool, err error) {
 	}
 	return
 }
+
+// Checks that a parameter can be passed as a non-trailing, and returns "*"
+// if it can't. See #697.
+func SafeErrorParam(param string) string {
+	if param == "" || param[0] == ':' || strings.IndexByte(param, ' ') != -1 {
+		return "*"
+	}
+	return param
+}