muc: the original stanza must be emitted

Otherwise other plugins don't know whether the message was forwarded or not.

src/converse-muc.js

@@ -1900,7 +1900,7 @@
                     this.model.createMessage(message, delay, original_stanza);
                     if (sender !== this.model.get('nick')) {
                         // We only emit an event if it's not our own message
-                        _converse.emit('message', message);
+                        _converse.emit('message', original_stanza);
                     }
                     return true;
                 }