fix: never sort the message before chat joining timestamp

This is to avoid sorting incoming messages that
are slightly in the past above system messages
about SecureJoin. SecureJoin messages are
timed according to smeared timestamp,
so even in the local tests they are in the future
by a few seconds.

src/chat.rs

@@ -930,6 +930,17 @@ SELECT id, rfc724_mid, pre_rfc724_mid, timestamp, ?, 1 FROM msgs WHERE chat_id=?
             .unwrap_or(0))
     }
 
+    /// Returns timestamp of us joining the chat if we are the member of the chat.
+    pub(crate) async fn join_timestamp(self, context: &Context) -> Result<Option<i64>> {
+        context
+            .sql
+            .query_get_value(
+                "SELECT add_timestamp FROM chats_contacts WHERE chat_id=? AND contact_id=?",
+                (self, ContactId::SELF),
+            )
+            .await
+    }
+
     /// Returns timestamp of the latest message in the chat,
     /// including hidden messages or a draft if there is one.
     pub(crate) async fn get_timestamp(self, context: &Context) -> Result<Option<i64>> {
@@ -1287,7 +1298,16 @@ SELECT id, rfc724_mid, pre_rfc724_mid, timestamp, ?, 1 FROM msgs WHERE chat_id=?
             sort_timestamp = last_msg_time;
         }
 
-        Ok(sort_timestamp)
+        if let Some(join_timestamp) = self.join_timestamp(context).await? {
+            // If we are the member of the chat, don't add messages
+            // before the timestamp of us joining it.
+            // This is needed to avoid sorting "Member added"
+            // or automatically sent bot welcome messages
+            // above SecureJoin system messages.
+            Ok(std::cmp::max(sort_timestamp, join_timestamp))
+        } else {
+            Ok(sort_timestamp)
+        }
     }
 }