fix #1730

`WHO #channel o` is supposed to return only server operators.
This is RFC1459 cruft; just return an empty list in this case.

irc/handlers.go

 		fields = fields.Add(field)
 	}
 
-	//TODO(dan): is this used and would I put this param in the Modern doc?
-	// if not, can we remove it?
-	//var operatorOnly bool
-	//if len(msg.Params) > 1 && msg.Params[1] == "o" {
-	//	operatorOnly = true
-	//}
+	// successfully parsed query, ensure we send the success response:
+	defer func() {
+		rb.Add(nil, server.name, RPL_ENDOFWHO, client.Nick(), origMask, client.t("End of WHO list"))
+	}()
+
+	// XXX #1730: https://datatracker.ietf.org/doc/html/rfc1459#section-4.5.1
+	// 'If the "o" parameter is passed only operators are returned according to
+	// the name mask supplied.'
+	// see discussion on #1730, we just return no results in this case.
+	if len(msg.Params) > 1 && msg.Params[1] == "o" {
+		return false
+	}
 
 	oper := client.Oper()
 	hasPrivs := oper.HasRoleCapab("sajoin")
 		}
 	}
 
-	rb.Add(nil, server.name, RPL_ENDOFWHO, client.nick, origMask, client.t("End of WHO list"))
 	return false
 }