feat: advance next UID even if connection fails while fetching

Connection sometimes fails while processing FETCH
responses. In this case `fetch_new_messages` exits early
and does not advance next expected UID even if
some messages were processed.

This results in prefetching the same messages
after reconnection and log messages
similar to
"Not moving the message ab05c85a-e191-4fd2-a951-9972bc7e167f@localhost that we have seen before.".

With this change we advance next expected UID
even if `fetch_new_messages` returns a network error.

src/download.rs

@@ -213,17 +213,18 @@ impl Session {
 
         let mut uid_message_ids: BTreeMap<u32, String> = BTreeMap::new();
         uid_message_ids.insert(uid, rfc724_mid);
-        let (last_uid, _received) = self
-            .fetch_many_msgs(
-                context,
-                folder,
-                uidvalidity,
-                vec![uid],
-                &uid_message_ids,
-                false,
-            )
-            .await?;
-        if last_uid.is_none() {
+        let (sender, receiver) = async_channel::unbounded();
+        self.fetch_many_msgs(
+            context,
+            folder,
+            uidvalidity,
+            vec![uid],
+            &uid_message_ids,
+            false,
+            sender,
+        )
+        .await?;
+        if receiver.recv().await.is_err() {
             bail!("Failed to fetch UID {uid}");
         }
         Ok(())