fix: Mark a message as delivered only after it has been fully sent out

[Hocuri]

Fix #8042

The problem was that after receiving the bcc_self'ed pre-message in receive_imf, the logic there only looked for a pending smtp-table-entry that matches the rfc724_mid, and if there was none then it thought "Great, apparently the message is fully sent out, we can mark it as delivered!".

But with pre-messages, the same message can have two smtp entries (one for the pre-message and one for the post-message), and the message should only be marked as delivered once both of them are sent out.

Now, I changed the logic to look for all entries with the same msg_id. This is actually the same SQL query used in smtp.rs, so, I extracted it into a new function; feel free to suggest a better name for it.

I tested on Android that it now works fine.

I'm not sure about a test - it would probably be possible to write a python test that tries to send a very large message, but it would take multiple minutes to complete depending on the speed of the internet, and it would depend on the server rejecting large messages.

There are a lot of other problems with sending large files, though:

• The pre-message is sent before the post-message, so that for the receiver it looks as if the message arrived, but stays in "downloading..." forever: Do not send pre-message if post-message sending failed #8063
• There is quite a time delay between clicking on "Send" and the outgoing message appearing in the chat
• The message shortly gets a letter icon right after it is sent
• I'm wondering if there is a way to give feedback to the user immediately if the message is too big
• It's unclear when exactly we want to send read receipts

See #8078 for the last four of them.

[iequidoo]

I'm not sure about a test - it would probably be possible to write a python test that tries to send a very large message, but it would take multiple minutes to complete depending on the speed of the internet, and it would depend on the server rejecting large messages.

This can be tested in Rust, you can pop the pre-message from the SMTP queue and pass it to receive_imf. This doesn't block the fix though, if you want, i can do a follow-up PR with a test.

[iequidoo]

Btw, the whole block can be moved to some MsgId::set_delivered_if_fully_sent(), but maybe not hiding the check inside some function is clearer...

[Hocuri]

I wrote a test, and checked that the test fails on main but passes with this PR, but I'll create a separate PR for the test so that it can be reviewed separately.