Show omemo UI if encryption is active

The UI should be shown when encryption is active in any case
so that the user can disable it.
If for any reason the jid of the contact is not in device_ids
the UI was not shown before. If addtionally the last
known state of encryption was active, the user saw no UI
and couldnt disable omemo. Because for the jid are no devices known
(hence not in device_ids) and omemo = active, because of security
omemo wouldnt let any messages be sent. The user had no
chance to come out of this state

omemo/__init__.py

@@ -312,13 +312,18 @@ class OmemoPlugin(GajimPlugin):
             self.ui_list[account_name] = {}
         state = self.get_omemo_state(account_name)
         my_jid = gajim.get_jid_from_account(account_name)
+        omemo_enabled = state.encryption.is_active(contact_jid)
+        if omemo_enabled:
+            log.debug(account_name + " => Adding OMEMO ui for " + contact_jid)
+            self.ui_list[account_name][contact_jid] = Ui(self, chat_control,
+                                                         omemo_enabled, state)
+            return
         if contact_jid in state.device_ids or contact_jid == my_jid:
             log.debug(account_name + " => Adding OMEMO ui for " + contact_jid)
-            omemo_enabled = state.encryption.is_active(contact_jid)
             self.ui_list[account_name][contact_jid] = Ui(self, chat_control,
                                                          omemo_enabled, state)
         else:
-            log.warn(account_name + " => No OMEMO dev_keys for " + contact_jid)
+            log.warn(account_name + " => No devices for " + contact_jid)
 
     def are_keys_missing(self, account_name, contact_jid):
         """ Used by the ui to set the state of the PreKeyButton. """