OMEMEO Messages without key should show an Error Message

Versions

• OS: Windows
• Gajim version: 1.1.2
• GTK version: 3.24.1
• Python-nbxmpp version: 0.6.9

Steps to reproduce the problem

Assume a multi device setup with Alice and Bob.

Bob is using Gajim on one Device and something else on another. Now Alice sends a Message encrypted with OMEMO, but does not trust Bob's Gajim Key.

Expected behavior

A Message in the Conversation with Alice should tell Bob "This Message was encrypted, but can not be decrypted" (In some untraceable cases a message like this was displayed, but this could not be reproduced)

Actual behavior

Gajim now does receive the encrypted message (in the XML-Console) but does not show anything to indicate an Error.