fix(channelserver): add fail ACKs to silent error paths to prevent client softlocks

Handlers that log errors and return without sending a MsgSysAck leave
the client waiting indefinitely. Add doAckSimpleFail/doAckBufFail to
14 error paths across 4 files, matching the pattern already used in
~70 other error paths across the codebase.

Affected handlers:
- handleMsgMhfGetCafeDuration (1 path)
- handleMsgMhfSavedata (1 path)
- handleMsgMhfArrangeGuildMember (3 paths)
- handleMsgMhfEnumerateGuildMember (5 paths)
- handleMsgSysLogin (4 paths)
- handleMsgSysIssueLogkey (1 path)

server/channelserver/handlers_data.go

@@ -22,6 +22,7 @@ func handleMsgMhfSavedata(s *Session, p mhfpacket.MHFPacket) {
 	characterSaveData, err := GetCharacterSaveData(s, s.charID)
 	if err != nil {
 		s.logger.Error("failed to retrieve character save data from db", zap.Error(err), zap.Uint32("charID", s.charID))
+		doAckSimpleFail(s, pkt.AckHandle, make([]byte, 4))
 		return
 	}
 	// Var to hold the decompressed savedata for updating the launcher response fields.