fix: onEventMessagesChanged: handle msgId == 0

This cause the message list to be empty when the chat gets opened,
and not update on some events.

Reproduction steps are roughly as follows:
1. Create two accounts
2. On Alice, send ~20 messages to Bob.
3. Switch to Bob's account and open the chat with Alice.
  Do not scroll to bottom.
4. Switch to Alice account and send another message to Bob.
5. Switch to Bob's account and open the chat with Alice.

You will see the `Failed to load message Msg#0 for account` error
in the console and the chat will be empty.

The bug was introduced in 7a968b6
(#4529).

The added `messageId > C.DC_MSG_ID_LAST_SPECIAL` in the first `if`
is purely for consistency and performance.
It's the second one that matters.

CHANGELOG.md

@@ -9,6 +9,7 @@
 ### Changed
 
 ### Fixed
+- message list being empty when opening a chat in some cases #4555
 - numpad "Enter" not working as regular "Enter" #4546
 - improve performance a little
 

packages/frontend/src/stores/messagelist.ts

@@ -922,6 +922,7 @@ class MessageListStore extends Store<MessageListState> {
     onEventMessagesChanged: this.scheduler.queuedEffect(
       async (messageId: number) => {
         if (
+          messageId > C.DC_MSG_ID_LAST_SPECIAL &&
           this.state.messageListItems.findIndex(
             m => m.kind === 'message' && m.msg_id === messageId
           ) !== -1
@@ -954,6 +955,7 @@ class MessageListStore extends Store<MessageListState> {
           // perhaps by moving `getLastKnownScrollPosition()`
           // to the render function of `MessageList`.
           if (
+            messageId > C.DC_MSG_ID_LAST_SPECIAL &&
             (await BackendRemote.rpc.getMessage(this.accountId, messageId))
               .state === C.DC_STATE_OUT_DRAFT
           ) {