fix: Mark a message as delivered only after it has been fully sent out (#8062)

Fix https://github.com/chatmail/core/issues/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'll add a test in a follow-up PR.

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
- 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

I'll open a follow-up issue for these.

src/receive_imf.rs

@@ -45,6 +45,7 @@ use crate::securejoin::{
     self, get_secure_join_step, handle_securejoin_handshake, observe_securejoin_on_other_device,
 };
 use crate::simplify;
+use crate::smtp::msg_has_pending_smtp_job;
 use crate::stats::STATISTICS_BOT_EMAIL;
 use crate::stock_str;
 use crate::sync::Sync::*;
@@ -582,14 +583,7 @@ pub(crate) async fn receive_imf_inner(
                 (rfc724_mid_orig, &self_addr),
             )
             .await?;
-        if !context
-            .sql
-            .exists(
-                "SELECT COUNT(*) FROM smtp WHERE rfc724_mid=?",
-                (rfc724_mid_orig,),
-            )
-            .await?
-        {
+        if !msg_has_pending_smtp_job(context, msg_id).await? {
             msg_id.set_delivered(context).await?;
         }
         return Ok(None);