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-repl/src/cmdline.rs

@@ -187,6 +187,7 @@ async fn log_msg(context: &Context, prefix: impl AsRef<str>, msg: &Message) {
         DownloadState::Available => " [⬇ Download available]",
         DownloadState::InProgress => " [⬇ Download in progress...]️",
         DownloadState::Failure => " [⬇ Download failed]",
+        DownloadState::Undecipherable => " [⬇ Decryption failed]",
     };
 
     let temp2 = timestamp_to_str(msg.get_timestamp());