fix: do not allow chat creation if decryption failed

src/receive_imf.rs

@@ -761,7 +761,9 @@ async fn add_parts(
         ShowEmails::from_i32(context.get_config_int(Config::ShowEmails).await?).unwrap_or_default();
 
     let allow_creation;
-    if mime_parser.is_system_message != SystemMessage::AutocryptSetupMessage
+    if mime_parser.decrypting_failed {
+        allow_creation = false;
+    } else if mime_parser.is_system_message != SystemMessage::AutocryptSetupMessage
         && is_dc_message == MessengerMessage::No
         && !context.get_config_bool(Config::IsChatmail).await?
     {

src/sync.rs

@@ -612,7 +612,7 @@ mod tests {
 
         // the same sync message sent to bob must not be executed
         let bob = TestContext::new_bob().await;
-        bob.recv_msg(&sent_msg).await;
+        bob.recv_msg_trash(&sent_msg).await;
         assert!(!token::exists(&bob, token::Namespace::Auth, "testtoken").await?);
 
         Ok(())

src/tests/verified_chats.rs

@@ -987,13 +987,10 @@ async fn test_verified_lost_member_added() -> Result<()> {
     assert_eq!(sent_msg.get_showpadlock(), true);
 
     // The message will not be sent to Fiona.
-    // Test that Fiona will not be able to decrypt it.
-    let fiona_rcvd = fiona.recv_msg(&sent).await;
-    assert_eq!(fiona_rcvd.get_showpadlock(), false);
-    assert_eq!(
-        fiona_rcvd.get_text(),
-        "[...] – [This message was encrypted for another setup.]"
-    );
+    // Test that Fiona will not be able to decrypt it
+    // and the message is trashed because
+    // we don't create groups from undecipherable messages.
+    fiona.recv_msg_trash(&sent).await;
 
     // Advance the time so Alice does not leave at the same second
     // as the group was created.