fix: receive_imf: Don't break 1:1 chat protection if received the verified Autocrypt key (#4597)

For example, broadcast list messages are sent unencrypted, but their Autocrypt header still contains
the verified key. Thus we're sure that we still can encrypt to the peer and there's no need to break
the existing protection.

src/tests/verified_chats.rs

@@ -1,7 +1,7 @@
 use anyhow::Result;
 use pretty_assertions::assert_eq;
 
-use crate::chat::{Chat, ProtectionStatus};
+use crate::chat::{add_contact_to_chat, create_broadcast_list, Chat, ProtectionStatus};
 use crate::chatlist::Chatlist;
 use crate::config::Config;
 use crate::constants::DC_GCL_FOR_FORWARDING;
@@ -12,7 +12,9 @@ use crate::mimefactory::MimeFactory;
 use crate::mimeparser::SystemMessage;
 use crate::receive_imf::receive_imf;
 use crate::stock_str;
-use crate::test_utils::{get_chat_msg, mark_as_verified, TestContext, TestContextManager};
+use crate::test_utils::{
+    check_msg_with_err, get_chat_msg, mark_as_verified, TestContext, TestContextManager,
+};
 use crate::{e2ee, message};
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
@@ -742,6 +744,45 @@ async fn test_create_oneonone_chat_with_former_verified_contact() -> Result<()>
     Ok(())
 }
 
+/// Some messages are sent unencrypted, but they mustn't break a verified chat protection.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_unencrypted() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = tcm.alice().await;
+    let bob = tcm.bob().await;
+    enable_verified_oneonone_chats(&[&alice]).await;
+    mark_as_verified(&alice, &bob).await;
+
+    let err_str = "This message is not encrypted. See 'Info' for more details";
+    let msg = tcm.send_recv_with_err(&bob, &alice, err_str, "hi").await;
+    assert!(!msg.get_showpadlock());
+    let alice_chat = Chat::load_from_db(&alice, msg.chat_id).await?;
+    assert!(alice_chat.is_protected());
+    assert!(!alice_chat.is_protection_broken());
+
+    let broadcast_id = create_broadcast_list(&bob).await?;
+    add_contact_to_chat(
+        &bob,
+        broadcast_id,
+        bob.add_or_lookup_contact(&alice).await.id,
+    )
+    .await?;
+    let sent_msg = bob.send_text(broadcast_id, "hi all").await;
+    let msg = alice.recv_msg(&sent_msg).await;
+    check_msg_with_err(&alice, &msg, err_str, "hi all").await;
+    assert!(!msg.get_showpadlock());
+    assert_eq!(msg.chat_id, alice_chat.id);
+    let alice_chat = Chat::load_from_db(&alice, msg.chat_id).await?;
+    assert!(alice_chat.is_protected());
+    assert!(!alice_chat.is_protection_broken());
+
+    alice
+        .golden_test_chat(alice_chat.id, "verified_chats_test_unencrypted")
+        .await;
+
+    Ok(())
+}
+
 // ============== Helper Functions ==============
 
 async fn assert_verified(this: &TestContext, other: &TestContext, protected: ProtectionStatus) {