fix: lookup_chat_by_reply(): Skip not fully downloaded and undecipherable messages (#4676)

Such a message may be assigned to a wrong chat (e.g. undecipherable group msgs often get assigned to
the 1:1 chat with the sender). Add `DownloadState::Undecipherable` so that messages referencing
undecipherable ones don't go to that wrong chat too. Also do not reply to not fully downloaded
messages. Before `Message.error` was checked for that purpose, but a message can be error for many
reasons.

deltachat-jsonrpc/src/api/types/message.rs

@@ -318,6 +318,7 @@ pub enum DownloadState {
     Done,
     Available,
     Failure,
+    Undecipherable,
     InProgress,
 }
 
@@ -327,6 +328,7 @@ impl From<download::DownloadState> for DownloadState {
             download::DownloadState::Done => DownloadState::Done,
             download::DownloadState::Available => DownloadState::Available,
             download::DownloadState::Failure => DownloadState::Failure,
+            download::DownloadState::Undecipherable => DownloadState::Undecipherable,
             download::DownloadState::InProgress => DownloadState::InProgress,
         }
     }