fix: return correct MsgId for malformed message tombstone

.execute() returns the number of affected rows,
in this case it is always 1 and MsgId(1) is returned
instead of the actual tombstone row ID.

src/receive_imf.rs

@@ -139,7 +139,7 @@ pub(crate) async fn receive_imf_inner(
 
             let row_id = context
                 .sql
-                .execute(
+                .insert(
                     "INSERT INTO msgs(rfc724_mid, chat_id) VALUES (?,?)",
                     (rfc724_mid, DC_CHAT_ID_TRASH),
                 )

src/receive_imf/tests.rs

@@ -322,7 +322,7 @@ async fn test_no_from() {
     let chats = Chatlist::try_load(&t, 0, None, None).await.unwrap();
     assert!(chats.get_msg_id(0).is_err());
 
-    receive_imf(
+    let received = receive_imf(
         context,
         b"Received: (Postfix, from userid 1000); Mon, 4 Dec 2006 14:51:39 +0100 (CET)\n\
                  To: bob@example.com\n\
@@ -335,8 +335,13 @@ async fn test_no_from() {
         false,
     )
     .await
+    .unwrap()
     .unwrap();
 
+    // Check that tombstone MsgId is returned.
+    assert_eq!(received.msg_ids.len(), 1);
+    assert!(!received.msg_ids[0].is_special());
+
     let chats = Chatlist::try_load(&t, 0, None, None).await.unwrap();
     // Check that the message is not shown to the user:
     assert!(chats.is_empty());