Send MDNs for messages deleted on the server

Now MarkseenMsgOnImap sends MDN even if it can't mark the message as
seen on the server.

To prevent multiple MDNs from being sent, MarkseenMsgOnImap is postponed
until the message is detected in a folder from which it is not going to
be moved.

src/message.rs

@@ -6,6 +6,7 @@ use lazy_static::lazy_static;
 use serde::{Deserialize, Serialize};
 
 use crate::chat::{self, Chat, ChatId};
+use crate::config::Config;
 use crate::constants::*;
 use crate::contact::*;
 use crate::context::*;
@@ -68,6 +69,40 @@ impl MsgId {
         self.0 == 0
     }
 
+    /// Returns message state.
+    pub async fn get_state(self, context: &Context) -> crate::sql::Result<MessageState> {
+        let result = context
+            .sql
+            .query_get_value_result("SELECT state FROM msgs WHERE id=?", paramsv![self])
+            .await?
+            .unwrap_or_default();
+        Ok(result)
+    }
+
+    /// Returns true if the message needs to be moved from `folder`.
+    pub async fn needs_move(self, context: &Context, folder: &str) -> Result<bool, Error> {
+        if !context.get_config_bool(Config::MvboxMove).await {
+            return Ok(false);
+        }
+
+        if context.is_mvbox(folder).await {
+            return Ok(false);
+        }
+
+        let msg = Message::load_from_db(context, self).await?;
+
+        if msg.is_setupmessage() {
+            // do not move setup messages;
+            // there may be a non-delta device that wants to handle it
+            return Ok(false);
+        }
+
+        match msg.is_dc_message {
+            MessengerMessage::No => Ok(false),
+            MessengerMessage::Yes | MessengerMessage::Reply => Ok(true),
+        }
+    }
+
     /// Put message into trash chat and delete message text.
     ///
     /// It means the message is deleted locally, but not on the server