fix: onEventMessagesChanged: handle msgId == 0

[WofWca]

This could cause the message list to not update on some events, but I have not seen a concrete example.

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.

Update: OK, this really does appear like this is causing the "empty chat issue". 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.

I apologize for such carelessness.

[nicodh]

What is DC_MSG_ID_LAST_SPECIAL? Is it documented somewhere? And what kind of bug does this fix?

[WofWca]

And what kind of bug does this fix?

Apologies, I updated the description: "This could cause the message list to not update on some events, but I have not seen a concrete example."
Update: I updated the description again. This fixes message list being empty sometimes.

What is DC_MSG_ID_LAST_SPECIAL?

We have "special" message IDs and "normal" message IDs. All special message IDs are <= than DC_MSG_ID_LAST_SPECIAL.

Is it documented somewhere?

Should be in core, but I haven't seen the docs specifically for this.

[nicodh]

Fixes the reported problem!

No need for apologize - regarding the number of contributions bugs can happen :-)

[ralphtheninja]

I apologize for such carelessness.

This is software development. It's impossible to foresee everything, even with colleagues reviewing the code etc. Things like this happens, even to the best developers :)