let's be compatible with XEP-0184 v1.0.

src/common/connection_handlers.py

@@ -1005,8 +1005,11 @@ class ConnectionHandlersBase:
         # We got our message's receipt
         if obj.receipt_received_tag and obj.session.control and \
         gajim.config.get_per('accounts', self.name, 'request_receipt'):
-            obj.session.control.conv_textview.hide_xep0184_warning(
-                obj.receipt_received_tag.getAttr('id'))
+            id_ = obj.receipt_received_tag.getAttr('id')
+            if not id_:
+                # old XEP implementation
+                id_ = obj.id_
+            obj.session.control.conv_textview.hide_xep0184_warning(id_)
 
         if obj.mtype == 'error':
             if not obj.msgtxt: