fix: do not fail to receive post-message with status updates for deleted webxdc

receive_imf should not fail in this case,
but trash the post-message and updates.

The problem with previously used message::rfc724_mid_exists check
was that rfc724_mid_exists may return a trashed message.

src/receive_imf.rs

@@ -835,21 +835,16 @@ UPDATE config SET value=? WHERE keyname='configured_addr' AND value!=?1
         {
             can_info_msg = false;
             if mime_parser.pre_message == PreMessageMode::Post
-                && let Some(msg_id) = message::rfc724_mid_exists(context, rfc724_mid_orig).await?
+                && let Some(msg) =
+                    Message::load_by_rfc724_mid_optional(context, rfc724_mid_orig).await?
             {
                 // The messsage is a post-message and pre-message exists.
                 // Assign status update to existing message because just received post-message will be trashed.
-                Some(
-                    Message::load_from_db(context, msg_id)
-                        .await
-                        .context("Failed to load webxdc instance that we just checked exists")?,
-                )
+                Some(msg)
             } else {
-                Some(
-                    Message::load_from_db(context, insert_msg_id)
-                        .await
-                        .context("Failed to load just created webxdc instance")?,
-                )
+                Message::load_from_db_optional(context, insert_msg_id)
+                    .await
+                    .context("Failed to load just created webxdc instance")?
             }
         } else if let Some(field) = mime_parser.get_header(HeaderDef::InReplyTo) {
             if let Some(instance) =