fix: return valid MsgId from receive_imf() when the message is replaced

receive_imf() calls add_parts()
which INSERTs or UPDATEs the message using UPSERT [1].
It then uses last_insert_rowid() to get
the ID of the inserted message.
However, it is incorrect to use last_insert_rowid()
if an UPDATE was executed instead of INSERT.
The solution is to use `RETURNING id` clause
to make the UPSERT statement return message ID in any case [2].

The fix is tested in test_webxdc_update_for_not_downloaded_instance()
and with a debug_assert!.

[1] https://www.sqlite.org/lang_UPSERT.html
[2] https://sqlite.org/forum/forumpost/9ce3bc1c4a85c15f

src/webxdc.rs

@@ -1177,7 +1177,7 @@ mod tests {
         assert_eq!(bob_instance.download_state, DownloadState::Available);
 
         // Bob downloads instance, updates should be assigned correctly
-        receive_imf_inner(
+        let received_msg = receive_imf_inner(
             &bob,
             &alice_instance.rfc724_mid,
             sent1.payload().as_bytes(),
@@ -1185,7 +1185,9 @@ mod tests {
             None,
             false,
         )
-        .await?;
+        .await?
+        .unwrap();
+        assert_eq!(*received_msg.msg_ids.get(0).unwrap(), bob_instance.id);
         let bob_instance = bob.get_last_msg().await;
         assert_eq!(bob_instance.viewtype, Viewtype::Webxdc);
         assert_eq!(bob_instance.download_state, DownloadState::Done);